Synthesis of bisquaraine dyes. Novel homologues of 1,2-squaraines bearing symmetrical and unsymmetrical structures

Article abstract of DOI:10.1039/b104059f

In order to investigate analogous structures of 1,2-squaraine dyes, bisquaraines 1 and 2 are newly prepared as their novel homologues. Symmetrical bisquaraine dye 1, in which the same heterocyclic components are introduced at the 3 and 3′ positions of the

Full text of DOI:10.1039/b104059f

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Synthesis of bisquaraine dyes. Novel homologues of 1,2-squaraines
bearing symmetrical and unsymmetrical structures
Yutaka Hyodo, Hiroyuki Nakazumi,* Shigeyuki Yagi and Kazuhisa Nakai
1
Department of Applied Materials Science, Graduate School of Engineering,
Osaka Prefecture University, Gakuen-cho 1-1, Sakai, Osaka 599-8531, Japan
Received (in Cambridge, UK) 9th May 2001, Accepted 29th August 2001
First published as an Advance Article on the web 17th October 2001
In order to investigate analogous structures of 1,2-squaraine dyes, bisquaraines 1 and 2 are newly prepared as their
novel homologues. Symmetrical bisquaraine dye 1, in which the same heterocyclic components are introduced at the
3 and 3Ј positions of the bisquaryl skeleton, is obtained by reaction of 4,4Ј-bi(3-isopropoxycyclobut-3-ene-1,2-dione)
3 with a series of heterocyclic compounds 5. The structure of one of the symmetrical dyes is confirmed by X-ray
structural analysis, showing a largely extended π-conjugation system over the whole molecule. The synthesis of
unsymmetrical dyes 2, in which different aromatic components are introduced, is established by the reactions of
5 with 3Ј-monosubstituted bisquarates 6. Each bisquaraine dye exhibits two absorption maxima separated by 56–75
nm, the lower-energy absorption of which is observed at 653–757 nm.
range of utility of SQ dyes. Another possibility for exploring
Introduction
new classes of SQ dyes lies in the modification of the central
Dye chemistry started at the end of 19th century, and has
cyclobutene moiety. Here we report novel homologues of
developed into various fields such as the evolution of synthesis,
1,2-SQ dyes, the bisquaraines, in which two heterocyclic com-
structural analysis, and computational chemistry of the de-
ponents are attached to a bisquaryl skeleton. We successfully
localized π-electron systems. Recently, many dyes possessing
useful functionalities have been synthesized and used for
materials. In the optoelectronics field, several optical properties
established selective methods to obtain the unsymmetrical dyes
2 as well as the symmetrical ones 1.
of organic dyes are required for applications: for example, the
Results and discussion
absorption maxima of dyes should correspond to the emitting
wavelengths of the light sources, and the absorption coefficients
are desired to be large enough for use with high efficiency.
In terms of such technical requirements, squaraine (SQ) dyes
have been attracting much interest because they exhibit large
and intense light absorptions and their absorption bands are
tunable by varying the constituent aromatic or heterocyclic
components.
Synthesis of symmetrical bisquaraine dyes
The synthesis of the symmetrical bisquaraine dyes 1a–d is
shown in Scheme 1. 4,4Ј-Bi(cyclobut-3-ene-1,2-dione) (bi-
squaryl) was first reported by Liebeskind et al. and obtained
using the palladium-catalyzed coupling reactions of cyclobut-
3-ene-1,2-diones.11 At first, we chose bisquaric acid 4 as a
candidate for the starting material to obtain the bisquaraine
dyes because a typical synthesis of SQ dyes starts with squaric
acid. We examined the condensation of 4 and 2 equivalents of
salts 5a–d under conditions similar to the preparation of 1,3-
SQ dyes [benzene–butan-1-ol 4 : 1 (v/v), a small amount
of quinoline, reflux], which afforded too many products to be
isolated by the usual procedures such as recrystallization and
column chromatography. One can see that this is because there
exist several tautomers of 4 which are produced by keto–enol
tautomerism. Thus, diisopropyl bisquarate 3, in which the
tautomerism is prevented by exchanging two acidic protons
with isopropyl groups, was employed as a precursor. The
reaction of bisquarate 3 and 2 equivalents of 5a in the presence
of triethylamine in CH2Cl2 at rt afforded bisquaraine dye 1a in
39% yield. The reaction proceeded under the mild conditions,
and the resultant crude dye was purified as usual by silica gel
column chromatography. By a similar procedure, the sym-
metrical bisquaraine dyes 1b–d were obtained in 36–67% yield
from 3 and 2 equivalents of 5b–d, respectively. These results
are summarized in Table 1. Although 1a was characterized by
1H NMR, 1b–d could not be clearly identified by 1H NMR due
to their low solubility in the common solvents, but this was
SQ dyes, in general, are classified into two types; 1,2- and 1,3-
disubstituted derivatives of squaric acid (3,4-dihydroxycyclo-
but-3-ene-1,2-dione). The 1,3-SQ dyes, which are often
regarded as cyanine dyes as to their localized electronic struc-
tures, were first reported by Treibs and Jacob more than three
decades ago,1 and their various derivatives and related com-
pounds have been reported because of interest in their unique
structures and chromophoric properties.2,3 On the other hand,
the 1,2-SQ dyes possess a different electronic structure from the
1,3-SQs, that is, two cross-conjugated π-electron systems from
the aromatic or heterocyclic donors to the carbonyl acceptors in
the squarate afford merocyanine-type chromophoric systems.2a
Thus, unique SQ chromophores promising variability of
electro- and/or photochemical properties have been regarded as
potential materials for optoelectronic applications such as
xerographic devices,4 solar cells,5 optical recording media,6,7 and
so on. However, they possess a severe problem of limited syn-
thetic methodology: SQ dyes are obtained by the condensation
of squaric acid with two equivalents of nucleophilic aromatic
or heterocyclic compounds,8 but the traditional synthetic
method offers only symmetrical SQ dyes, in which the same
aromatic or heterocyclic components are attached to the cyclo-
butene ring. Recently, Law and Terpetschnig independently
explored novel methods to obtain unsymmetrical 1,3-SQ
dyes,9,10 and these synthetic breakthroughs should extend the
1
possible in CF3COOD. In the H NMR spectrum of 1a, both
indoline components are magnetically equivalent, indicating
the highly symmetrical structure of the bisquaraine dye.
DOI: 10.1039/b104059f
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830
This journal is © The Royal Society of Chemistry 2001
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Fig. 1 (a) ORTEP drawing of the symmetrical bisquaraine dye 1a.
All hydrogen atoms are omitted for clarity. (b) Selected bond lengths
of 1a. Crystallographic numbering scheme is used.
large extension of the π-conjugation system from one indoline
moiety to the other. As shown in Fig. 1(b), the bond lengths
of N(1)–C(6), C(6)–C(5), C(5)–C(4), C(4)–C(1) and C(1)–C(20)
are within the range 1.35–1.43 Å and exhibit a conjugated
double-bond character. On the other hand, the bonds C(1)–
C(2) and C(2)–C(3) are relatively longer and show a typical
single-bond length, indicating that they are not likely to partici-
pate in the polymethine π-conjugation of the chromophore.
Scheme 1
The crystal structural analysis of the bisquaraine dye 1a
The structure of 1a was confirmed by X-ray crystallography,
and the ORTEP drawing of 1a is shown in Fig. 1(a). The dye
1a has C2 rotational symmetry. The planarity of 1a permits a
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Table 1 Preparation, absorption maxima and extinction coefficients of the bisquaraine dyes 1 and 2
X1
X2
Yield (%)
39
λmax a/nm
logεa
657
601
≈550
4.87
1a
1b
4.73
b
653
595
≈550
4.92
67
4.73
b
692
628
≈600
5.04
1c
1d
41
36
70
4.79
b
757
682
≈620
5.14
4.76
b
653
598
≈585
5.01
2a
2b
4.85






b
672
613
≈600
5.02


50
4.82
b







705
641
≈550
5.10
2c
2d
50
38
4.82
b


640
600
4.71
4.68





2e
2f
70
33
648
620
4.73
4.72


642
604
4.70
4.67





2g
2h
30
35
649
620
4.73
4.72


656
620
4.70
4.61





2i
30
673
630
4.73
4.67
a In CHCl3 at 298 K within visible–near-IR region. b Shoulder.
Scheme 2. We examined the condensation of bisquarate 3 with 1
equivalent of 5a to obtain the monosubstituted bisquarate 6a,
but, contrary to our expectation, the symmetrical bisquaraine
dye 1a was exclusively formed. This is most likely because the
intermediate 6a is not less reactive than bisquarate 3. Therefore,
another route to prepare the monosubstituted bisquarate was
examined. The reaction of indolium 5a with 1 equivalent of
Synthesis of unsymmetrical bisquaraine dyes
Monosubstituted bisquarates should offer the opportunity for
stepwise introduction of different heterocyclic moieties into the
bisquaryl skeleton. In order to explore a reliable synthesis for
unsymmetrical bisquaraine dyes, we examined the synthesis of
the monosubstituted bisquarate intermediate 6a, as shown in
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830
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reaction conditions similar to those for the synthesis of the
symmetrical bisquaraine dyes (NEt3, CH2Cl2, rt). The same
reaction steps beginning with dialkylanilines and 3,4-dichloro-
cyclobut-3-ene-1,2-dione to yield the monosubstituted squar-
ates 6b–d were also successful, and the subsequent reactions
of 5b and 5c with 6b–d afforded the unsymmetrical squaraines
2d–i in 30–70% yield, respectively. The results are summarized
1
in Table 1. The structure of each dye was confirmed by H
NMR, IR, UV–vis, and FAB-MS spectroscopy as well as
1
elemental analysis. As a typical example, the H NMR spec-
trum of 2c is shown in Fig. 2. The signal of each proton was
assigned by 1H decoupling, 1H–1H COSY and NOE techniques.
The spectrum clearly shows that 2c possesses two different
heterocyclic components, the indoline and quinoline rings.
One may possibly expect formation of a mixture of 1a and 1d in
this reaction, but the results of the FAB-MS spectrum and
elemental analysis also support the unsymmetrical structure 2c.
Although the structure of compound 2c has not yet been con-
firmed by X-ray crystallographic analysis, the NOE correlations
(shown by arrows in Fig. 2) indicate that both exo-double
bonds attached to the indoline and quinoline rings adopt
the E configuration, as seen in the X-ray structure of 1a. The
possibility of a mixture of two symmetrical squaraine dyes can
also be excluded based on the following experimental evidence:
the dye 2a possesses a different Rf-value on silica gel thin-layer
chromatography [CH2Cl2–MeOH 40 : 1 (v/v)] from those of
the dyes 1a and 1b (0.17, 0.63 and 0.27 for 2a, 1a and 1b,
respectively), and the presence of only one spot on the TLC
plate for 2a indicated that the isolated dye 2a was a single
product. For the other unsymmetrical dyes, similar results were
obtained in the TLC study.
UV–vis absorption and fluorescence emission properties of
bisquaraine dyes
Typical absorption spectra of the bisquaraine dyes 1a, 1d,
and 2c are shown in Fig. 3, and the UV–vis spectral data of
all the dyes are summarized in Table 1. Characteristic is that all
these bisquaraine dyes have two broad absorption bands at
longer wavelengths, although typical squaraine dyes possess
single, sharp absorption maxima.12 For these three compounds
the two absorption maxima wavelengths differ by 56 to 75 nm,
and the intensity ratios of the longer-wavelength absorption
to the second one are 1.4–2.4. Taking into consideration that
the PPP (Pariser–Parr–Pople) MO calculations for 1a, 1d, and
2c yielded single lowest-energy transitions at 633, 727, and
Scheme 2
3,4-dichlorocyclobut-3-ene-1,2-dione afforded 3-(N-butyl-3,3-
dimethylindolin-2-ylidenemethyl)-4-chlorocyclobut-3-ene-1,2-
dione 7a in 47% yield. The palladium-catalyzed cross-coupling
reaction of 7a with the (tributyl)stannylcyclobutene-1,2-dione 8
afforded the intermediate 6a in 10% yield.
The reaction of 6a with 5b–d afforded the unsymmetrical
bisquaraine dyes 2a–c in 50–70% yield, respectively, under
Fig. 2 1H NMR spectrum (500 MHz) and NOE correlations of the unsymmetrical bisquaraine dye 2c in CDCl3 at 298 K.
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830
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Table 2 Fluorescence properties of the bisquaraine dyes 1 and 2a
also achieved by using the monosubstituted intermediate 6.
Thus, a wide range of combinations of aromatic and hetero-
cyclic components at the 3 and 3Ј positions were made possible,
leading to tuning of the absorption maxima over ca. 100 nm
(653–757 nm). The results obtained here have great implications
in the search for novel structures of squaraine dyes and related
compounds and, furthermore, should open the way to new
families of polymethine dyes.
Compound
Fex/nmb
Fem/nmc
Lifetime/ns
1a
1b
1c
1d
2a
2b
2c
2d
2e
2f
653.2, ≈600 (sh)
651.6, ≈590 (sh)
690.4, 624.8
758.8
652.0, 600.0
685.6
680.8
712.0, ≈800 (sh)
777.2
681.6, ≈770 (sh)
696.4, ≈770 (sh)
726.4, ≈800 (sh)
686.0
698.4
693.6
2.9
1.1
2.3
d
1.1
d
670.4, 618.0
d
d
d
712.4, 692.0, 650.0
650.4, ≈610 (sh)
651.2, ≈610 (sh)
650.4, ≈610 (sh)
649.6, ≈630 (sh)
689.2, ≈640 (sh)
685.2, ≈660 (sh)
Experimental
1.1
General
d
2g
2h
2i
686.0
713.2
721.6
1H NMR spectra were recorded on JEOL GX-270 (270 MHz)
or JEOL A-500 (500 MHz) FT-NMR spectrometers, and
chemical shifts are reported in ppm downfield from the TMS
signal (δ 0) as internal standard. 1H Decoupling, 1H–1H COSY
and NOE spectra were taken at 500 MHz. EI mass spectra were
obtained on a Shimadzu QP-5000 mass spectrometer. FAB
mass spectra were obtained on a Finnigan MAT TSQ-70 mass
spectrometer using 3-nitrobenzyl alcohol as matrix. IR spectra
were recorded on a Horiba FT-200 spectrometer using
KBr pellets. UV–vis absorption spectra were recorded on a
Shimadzu UV-3100 spectrometer. Fluorescence spectra were
recorded on a Shimadzu RF-5000 spectrofluorophotometer.
Fluorescence-lifetime analyses were carried out with a Horiba
NAES 550 nanosecond fluorometer. Elemental analyses were
carried out with a Yanaco CHN-CORDER MT-3 recorder.
d
d
a 2.0 µM CHCl3 solution at 15 ЊC. Fex is the maximum wavelength in
the excitation spectrum monitored at the emission maximum (Fem).
c Fem is the fluorescence maximum in the emission spectrum excited at
b
λmax.
d Not measured due to low intensity.
Materials and solvents
4,4Ј-Bi(3-hydroxycyclobut-3-ene-1,2-dione) 4 (bisquaric acid)
and 4,4Ј-bi(3-isopropoxycyclobut-3-ene-1,2-dione)
3 (diiso-
propyl bisquarate) were synthesized according to Liebeskind’s
procedure cited in ref. 11. Deuterated chloroform and trifluoro-
acetic acid were purchased from Aldrich. Chloroform used for
UV–vis spectral analyses was of spectroscopic grade.
Fig. 3 UV–vis absorption spectra of 1a, 1d and 2c in CHCl3 at 298 K.
680 nm ( f = 2.711, 2.490, and 2.504), respectively, these peak
splittings are likely to be based on the vibrational structures.
The absorption maxima of the symmetrical and unsymmetrical
dyes are observed in the range 640–757 nm, with extinction
coefficients of ≈105 L cmϪ1 molϪ1: the absorption maxima of
the dyes depend on the aromatic and heterocyclic moieties.
It is noteworthy that the longest-wavelength absorption of the
unsymmetrical dye is at an average wavelength of the two
corresponding symmetrical dyes. For example, the absorption-
maximum wavelength of 2b shows a half-value of the sum of
the wavelengths of 1a and 1c. The same tendency was found in
the calculated values of λmax obtained by the PPP MO method.
The emission maxima (Fem), excitation maxima (Fex), and
fluorescence lifetimes of 1 and 2 in the fluorescence spectra are
summarized in Table 2. The fluorescence emissions observed
at the Fem by excitation at the λmax of 1 and 2 exhibited
much larger intensities than those observed by excitation at
the shorter wavelength of the absorption bands of 1 and 2. The
fluorescence lifetimes in solution (ca. 1–3 ns) were similar to
that of a typical squarylium dye.13 Proximity between the λmax
and the Fex as well as the single-component fluorescence lifetime
also suggests that the split lowest-energy absorptions are due to
vibrational modes of the electronic structures.
4,4Ј-Bi[3-(1-butyl-3,3-dimethylindolin-2-ylidenemethyl)cyclobut-
3-ene-1,2-dione] 1a
To a dispersed solution of 1-butyl-2,3,3-trimethylindolium
iodide 5a (0.689 g, 2.01 mmol) in CH2Cl2 (20 mL) was
added NEt3 (0.28 mL), followed by dropwise addition of a
solution of bi(3-isopropoxycyclobut-3-ene-1,2-dione) 3 (0.278
g, 1.00 mmol) in CH2Cl2 (20 mL). The reaction mixture
was stirred for 2 h at rt, and then the solvent was removed on
a rotary evaporator. The residue was purified by silica gel
chromatography (CH2Cl2 as eluent), and further purification by
recrystallization from CH2Cl2–hexane afforded crystals of 1a
1
(0.231 g, 0.393 mmol, 39%), mp 278 ЊC (decomp.); H NMR
(270 MHz; CDCl3) δ 0.99 (t, J = 7.3 Hz, 6 H), 1.47–1.69 (m,
4 H), 1.72 (s, 12 H), 1.78–1.86 (m, 4 H), 4.17 (t, J = 7.3 Hz, 4 H),
7.05 (d, J = 7.3 Hz, 2 H), 7.18 (d, J = 7.3 Hz, 2 H), 7.30–7.37
(m, 6 H); IR (KBr) ν 1726, 1722, 1697 cmϪ1; FAB MS m/z 589
([M ϩ H]ϩ) (Calc. for C38H40N2O4ؒ0.5H2O: C, 76.36; H, 6.91;
N, 4.69. Found: C, 75.88; H, 6.79; N, 4.47%).
4,4Ј-Bi[3-(3-butyl-2,3-dihydrobenzothiazol-2-ylidenemethyl)-
cyclobut-3-ene-1,2-dione] 1b
To a dispersed solution of 3-butyl-2-methylbenzothiazolium
iodide 5b (0.670 g, 2.01 mmol) in CH2Cl2 (20 mL) was added
NEt3 (0.28 mL), followed by dropwise addition of a solution of
diester 3 (0.278 g, 1.00 mmol) in CH2Cl2 (20 mL). The reaction
mixture was stirred for 2 h at rt, and a precipitate with metallic
luster was produced, which was separated by filtration, washed
with water, and dried in vacuo over silica gel to afford crystals of
1b (0.382 g, 0.671 mmol, 67%), mp 314 ЊC (decomp.); 1H NMR
(270 MHz; CF3COOD) δ 1.01–1.09 (m, 6 H), 1.58–1.66 (m,
4 H), 1.90–2.20 (m, 4 H), 4.61 (t, J = 7.6 Hz, 2 H), 4.91 (t, J = 7.9
Conclusions
We demonstrate here the first synthesis of novel bisquaraine
dyes which can be regarded as homologues of 1,2-SQ dyes.
Diisopropyl bisquarate 3 easily reacted with two equivalents of
heterocyclic compounds 5 to afford the symmetrical bisquar-
aine dyes 1a–d. The structure was confirmed by X-ray crystal-
lographic analysis for 1a, the planarity of which showed a large
extension of π-conjugation from one heterocyclic component to
the other. The selective synthesis of the unsymmetrical dyes was
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830
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Hz, 2 H), 7.60–7.76 (m, 4 H), 7.81–7.97 (m, 3 H), 8.06–8.13 (m,
3 H); IR (KBr) ν 1712, 1693 cmϪ1; FAB MS m/z 569 ([M ϩ H]ϩ)
(Calc. for C32H28N2O4S2: C, 67.58; H, 4.96; N, 4.92. Found:
C, 67.75; H, 4.93; N, 4.80%).
Symmetrical bisquaraine dyes 1c and 1d were prepared by the
same procedure outlined above for 1b, using the salts 5c and 5d.
3-(2,3,6,7-Tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-4-
chlorocyclobut-3-ene-1,2-dione 7d
This compound was synthesized in a similar manner to 7b in
1
35% yield, mp 209 ЊC (decomp.); H NMR (CDCl3) δ 1.99
(quint, J = 5.9 Hz, 2 H), 2.78 (t, J = 5.9 Hz, 4 H), 3.37 (t, J = 5.9
Hz, 4 H), 7.70 (s, 2 H); IR (KBr) ν 1774, 1749 cmϪ1 (C᎐O); EI
᎐
MS (m/z) 289 (Mϩ ϩ 2, 5%), 287 (Mϩ, 16), 233 (Mϩ ϩ 2 Ϫ 2CO,
34), 231 (Mϩ Ϫ 2CO, 100); this compound was used for the
following reaction without further purification.
4,4Ј-Bi[3-(1-butyl-1,2-dihydroquinolin-2-ylidenemethyl)-
cyclobut-3-ene-1,2-dione] 1c. 41% yield; mp 308 ЊC (decomp.);
1H NMR (270 MHz; CF3COOD) δ 1.09–1.16 (m, 6 H), 1.65–
1.79 (m, 4 H), 2.05–2.25 (m, 4 H), 4.84 (m, 4 H), 5.15 (m, 2 H),
7.75–7.80 (m, 1 H), 8.01–8.07 (m, 6 H), 8.25–8.38 (m, 2 H),
8.48–8.92 (m, 3 H); IR (KBr) ν 1710, 1697 cmϪ1; FAB MS
m/z 557 ([M ϩ H]ϩ) (Calc. for C36H32N2O4: C, 77.68; H, 5.79;
N, 5.03. Found: C, 77.39; H, 5.79; N, 4.79%).
3-(1-Butyl-3,3-dimethylindolin-2-ylidenemethyl)-3Ј-isopropoxy-
4,4Ј-bis(cyclobut-3-ene-1,2-dione) 6a
To a mixture of 7a (1.69 g, 5.12 mmol) and 3-isopropoxy-4-
(tributylstannyl)cyclobut-3-ene-1,2-dione 8 (2.20 g, 5.14 mmol)
in acetonitrile (30 mL) was added (PhCH2)PdCl(PPh3)2
(0.194 g, 5 mol% for 7a) and CuI (0.049 g, 5 mol% for 7a),
and the mixture was stirred for 4 h at 50 ЊC under nitrogen
atmosphere. After cooling, the reaction mixture was washed
with hexane, and the solvent was removed on a rotary evapor-
ator. The residue was dissolved in CH2Cl2 (20 mL), and a small
amount of activated carbon powder was added. The mixture
was heated at reflux for 1 h and filtered through Celite powder.
The filtrate was evaporated, and the residue was purified by
silica gel column chromatography (CH2Cl2 as eluent), followed
by recrystallization from CH2Cl2–hexane to afford crystals of
6a (0.232 g, 0.536 mmol, 10%), mp 153–154 ЊC; 1H NMR (270
MHz; CDCl3) δ 0.93 (t, J = 7.3 Hz, 3 H), 1.37–1.60 (m, 8 H),
1.62 (s, 6 H), 1.69–1.78 (m, 2 H), 4.70 (t, J = 7.3 Hz, 2 H), 5.58
(t, J = 6.1 Hz, 1 H), 6.95 (s, 1 H), 7.01 (d, J = 7.9 Hz, 1 H), 7.16
(m, 1 H), 7.26–7.32 (m, 2 H); IR (KBr) ν 1788, 1743, 1736, 1728
cmϪ1; EI MS m/z 433 (Mϩ, 1.4%), 334 (Mϩ Ϫ 2CO Ϫ C3H7,
100) (Calc. for C26H27NO5: C, 72.04; H, 6.28; N, 3.23. Found:
C, 72.23; H, 6.41; N, 3.29%).
4,4Ј-Bi[3-(1-butyl-1,4-dihydroquinolin-4-ylidenemethyl)-
cyclobut-3-ene-1,2-dione] 1d. 36% Yield; mp 305 ЊC (decomp.);
1H NMR (270 MHz; CF3COOD) δ 1.07–1.14 (m, 6 H), 1.65–
1.80 (m, 4 H), 2.05–2.25 (m, 4 H), 4.82 (m, 4 H), 5.14 (m, 2 H),
7.73–7.79 (m, 1 H), 7.98–8.07 (m, 6 H), 8.24–8.37 (m, 2 H),
8.44–8.91 (m, 3 H); IR (KBr) ν 1708, 1693 cmϪ1; FAB MS
m/z 557 ([M ϩ H]ϩ) (Calc. for C36H32N2O4: C, 77.68; H, 5.79; N,
5.03. Found: C, 77.60; H, 5.73; N, 4.88%).
3-(1-Butyl-3,3-dimethylindolin-2-ylidenemethyl)-4-chlorocyclo-
but-3-ene-1,2-dione 7a
To a mixture of 5a (3.91 g, 11.4 mmol) and 3,4-dichlorocyclo-
but-3-ene-1,2-dione14 (1.71 g, 11.3 mmol) in benzene (40 mL)
was added dropwise 1.6 mL of NEt3, and the mixture was
stirred for 2 h at rt. Then, the solvent was removed on a rotary
evaporator, and the residue was purified by silica gel column
chromatography (CH2Cl2 as eluent), followed by recrystalliz-
ation from CH2Cl2–hexane to afford crystals of 7a (1.75 g, 5.31
mmol, 47%), mp 102.3–103.1 ЊC; 1H NMR (270 MHz; CDCl3)
δ 1.03 (t, J = 7.3 Hz, 3 H), 1.41–1.59 (m, 2 H), 1.66 (s, 6 H),
1.70–1.82 (m, 2 H), 3.95 (t, J = 7.3 Hz, 2 H), 5.56 (s, 1 H), 7.05
(d, J = 7.3 Hz, 1 H), 7.18 (t, J = 7.3 Hz, 1 H), 7.31–7.36 (m, 2 H);
IR (KBr) ν 1767, 1727 cmϪ1; EI MS m/z 331 (Mϩ ϩ 2, 10%), 329
(Mϩ, 29), 273 (Mϩ Ϫ 2CO, 72), 258 ([M Ϫ 2CO Ϫ CH3]ϩ, 72)
(Calc. for C19H20ClNO2: C, 69.19; H, 6.11; N, 4.25. Found:
C, 68.81; H, 6.14; N, 4.25%).
3-[4-(Diethylamino)phenyl]-3Ј-isopropoxy-4,4Ј-bis(cyclobut-3-
ene-1,2-dione) 6b
3-[4-(Diethylamino)phenyl]-4-chlorocyclobut-3-ene-1,2-dione
7b (1.69 g, 5.12 mmol), 3-isopropoxy-4-(tributylstannyl)cyclo-
but-3-ene-1,2-dione (2.20 g, 5.14 mmol), (Ph3P)2Pd(CH2Ph)Cl
(0.194 g, 5 mol%) and CuI (0.049 g, 5 mol%) were dissolved in
30 mL of acetonitrile under nitrogen atmosphere. After being
refluxed for 4 h, the reaction mixture was cooled to room
temperature and poured into hexane to remove tributylstannyl
chloride. The hexane layer, immiscible with acetonitrile, was
removed and the acetonitrile layer was evaporated. The residue
was dissolved in CH2Cl2, treated with activated carbon, and the
solution was refluxed. The suspension was filtered through
Celite and the filtrate was evaporated. The residue was re-
crystallized from CH2Cl2–hexane to give the purple solid 6b
(0.23 g, 98%), mp 137 ЊC (decomp.); MS (m/z) 367 (Mϩ, 14%),
213 (100).
3-[4-(Diethylamino)phenyl]-4-chlorocyclobut-3-ene-1,2-dione 7b
To a CH2Cl2 (20 mL) solution of 3,4-dichlorocyclobut-3-ene-
1,2-dione14 (1.51 g, 10 mmol) was added dropwise a CH2Cl2
solution (10 mL) of N,N-diethylaniline, and the mixture was
stirred at rt for 3 h. Then, the solvent was removed and the
residue was purified by column chromatography (CH2Cl2 as
eluent) to give 7b as the yellow solid in 73% yield, mp 152 ЊC
1
(decomp.); H NMR (CDCl3) δ 1.24 (t, J = 7.3 Hz, 6 H), 3.48
Compounds 6c and 6d were prepared in similar manner and
used in the next step without further purification.
(q, J = 7.3 Hz, 4 H), 6.72 (d, J = 9.2 Hz, 2 H), 8.11 (d, J = 9.2 Hz,
2 H); IR (KBr) ν 1738, 1733 cmϪ1 (C᎐O); EI MS m/z 265
᎐
(Mϩ ϩ 2, 7%), 263 (Mϩ, 22), 209 (Mϩ ϩ 2 Ϫ 2CO, 11), 207
(Mϩ Ϫ 2CO, 38), 194 (Mϩ ϩ 2 Ϫ 2CO Ϫ CH3, 35), 192 (Mϩ Ϫ
2CO Ϫ CH3, 100) (Calc. for C14H14ClNO2: C, 63.78; H, 5.35;
N, 5.31. Found: C, 63.42; H, 5.43; N, 5.47%).
3-[4-(Dibutylamino)phenyl]-3Ј-isopropoxy-4,4Ј-bis(cyclobut-
3-ene-1,2-dione) 6c. Yield 80%; mp 75–80 ЊC; MS (m/z) 423
(Mϩ, 11%), 367 ([M Ϫ C4H9]ϩ, 8), 324 ([M Ϫ C4H9 Ϫ C3H7]ϩ,
14).
3-[4-(Dibutylamino)phenyl]-4-chlorocyclobut-3-ene-1,2-dione 7c
3-(2,3,6,7-Tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-
3Ј-isopropoxy-4,4Ј-bis(cyclobut-3-ene-1,2-dione) 6d. Yield 85%;
mp 149–151 ЊC; MS (m/z) 391 (Mϩ, 1.6%), 213 (100).
This compound was synthesized in a similar manner to 7b in
22% yield, mp 80–81 ЊC; 1H NMR(CDCl3) δ 0.98 (t, J = 7.3 Hz,
6 H), 1.39 (sextet, J = 7.3 Hz, 4 H), 1.63 (quint, J = 7.3 Hz, 4 H),
3.40 (t, J = 7.3 Hz, 4 H), 6.76 (d, J = 9.2 Hz, 2 H), 8.13 (d, J = 9.2
Hz, 2 H); IR (KBr) ν 1795 (C᎐O), 1759 cmϪ1 (C᎐O); FAB-MS
3-(3-Butyl-2,3-dihydrobenzothiazol-2-ylidenemethyl)-3Ј-(1-
butyl-3,3-dimethylindolin-2-ylidenemethyl)-4,4Ј-bis(cyclobut-3-
ene-1,2-dione) 2a
᎐
᎐
m/z 321 (Mϩ ϩ 2, 26%), 319 (Mϩ, 100), 265 ([M Ϫ 2CO]ϩ ϩ 2,
37), 263 ([M Ϫ 2CO]ϩ, 81) (Calc. for C18H22ClNO2: C, 67.60; H,
6.93; N, 4.38. Found: C, 67.79; H, 7.00; N, 4.45%).
To a dispersed solution of 5b (0.067 g, 0.20 mmol) in CH2Cl2
(4 mL) was added 0.1 mL of NEt3, and then a solution of 6a
2828
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830

View Article Online
(0.087 g, 0.20 mmol) in CH2Cl2 (4 mL) was added dropwise.
The mixture was stirred for 2 h at rt. The solvent was removed
on a rotary evaporator, and the residue was purified by silica
gel column chromatography (CH2Cl2 as eluent), followed by
recrystallization from CH2Cl2–hexane to afford crystals of 2a
(0.082 g, 0.14 mmol, 70%), mp 292 ЊC (decomp.); 1H NMR (270
MHz; CDCl3) δ 0.99 (t, J = 7.3 Hz, 3 H), 1.03 (t, J = 7.3 Hz,
3 H), 1.50–1.63 (m, 4 H), 1.71 (s, 6 H), 1.81–1.94 (m, 4 H), 4.14
(t, J = 7.3 Hz, 2 H), 4.29 (t, J = 7.3 Hz, 2 H), 7.03 (d, J = 7.3 Hz,
1 H), 7.16 (d, J = 7.3 Hz, 1 H), 7.26–7.36 (m, 6 H), 7.46 (t,
J = 7.3 Hz, 1 H), 7.64 (d, J = 7.3 Hz, 1 H); IR (KBr) ν 1726,
1722, 1697 cmϪ1; FAB MS m/z 579 ([M ϩ H]ϩ) (Calc. for
C35H34N2O4S: C, 72.64; H, 5.92; N, 4.84. Found: C, 72.90; H,
5.92; N, 4.94%).
(m, 9 H), 1.25–1.67 (m, 10 H), 1.91 (quint, J = 7.9 Hz, 2 H), 3.40
(q, J = 7.9 Hz, 4 H), 4.31 (t, J = 7.9 Hz, 2 H), 6.75 (d, J = 9.2 Hz,
2 H), 7.26–7.38 (m, 3 H), 7.49 (t, J = 7.9 Hz, 1 H), 7.68 (d,
J = 7.3 Hz, 1 H), 8.45 (d, J = 9.2 Hz, 2 H); IR (KBr) ν 1726, 1710
cmϪ1 (C᎐O); FAB MS (m/z) 569 (Mϩ ϩ H, 100%), 568 (Mϩ, 97)
᎐
(Calc. for C34H36N2O4S ϩ 0.2H2O: C, 71.35; H, 6.41; N, 4.89.
Found: C, 71.28; H, 6.43; N, 4.83%).
3-[4-(Dibutylamino)phenyl]-3Ј-(1-butyl-1,2-dihydroquinolin-
2-ylidenemethyl)-4,4Ј-bis(cyclobut-3-ene-1,2-dione) 2g. Yield
30%; mp 250 ЊC (decomp.); 1H NMR (CDCl3) δ 0.98 (t, J = 7.3
Hz, 3 H), 1.11 (t, J = 7.3 Hz, 6 H), 1.21–1.76 (m, 12 H), 3.36
(q, J = 7.3 Hz, 4 H), 4.47 (t, J = 7.3 Hz, 2 H), 6.75 (d, J = 9.2 Hz,
2 H), 7.09 (s, vinyl H, 1 H), 7.47 (t, J = 7.3 Hz, 1 H), 7.61–7.74
(m, 3 H), 7.82 (d, J = 9.8 Hz, 1 H), 8.39 (d, J = 9.2 Hz, 2 H), 8.91
Unsymmetrical bisquaraine dyes 2b–i were prepared by the
general procedure outlined for 2a.
(d, J = 9.8 Hz, 1 H); IR (KBr) ν 1733, 1714 cmϪ1 (C᎐O);
᎐
FAB MS (m/z) 563 (Mϩ ϩ H, 100%), 562 (Mϩ, 74) (Calc. for
C36H38N2O4 ϩ 0.75H2O: C, 75.04; H, 6.91; N, 4.86. Found: C,
75.10; H, 6.77; N, 4.69%).
3-(1-Butyl-3,3-dimethylindolin-2-ylidenemethyl)-3Ј-(1-butyl-1,2-
dihydroquinolin-2-ylidenemethyl)-4,4Ј-bis(cyclobut-3-ene-1,2-
dione) 2b
3-(2,3,6,7-Tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-
3Ј-(3-butyl-2,3-dihydrobenzothiazol-2-ylidenemethyl)-4,4Ј-bis-
(cyclobut-3-ene-1,2-dione) 2h. Yield 35%; 1H NMR (CDCl3)
δ 1.06 (t, J = 7.3 Hz, 3 H), 1.52–2.23 (m, 8 H), 2.81 (quint,
J = 6.2 Hz, 4 H), 3.36 (t, J = 6.7 Hz, 4 H), 4.30 (t, J = 7.3 Hz,
2 H), 7.26–7.38 (m, 2 H), 7.45 (m, 2 H), 7.66 (d, J = 7.9 Hz,
Yield 50%; mp 283 ЊC (decomp.); 1H NMR (270 MHz; CDCl3)
δ 0.99 (t, J = 7.3 Hz, 3 H), 1.10 (t, J = 7.3 Hz, 3 H), 1.48–1.66 (m,
4 H), 1.71 (s, 6 H), 1.76–1.95 (m, 4 H), 4.15 (t, J = 7.3 Hz, 2 H),
4.46 (t, J = 7.3 Hz, 2 H), 7.03 (d, J = 7.3 Hz, 1 H), 7.16 (d, J = 7.3
Hz, 1 H), 7.26–7.42 (m, 5 H), 7.57–7.75 (m, 4 H), 8.90 (d, J = 9.8
Hz, 1 H); IR (KBr) ν 1724, 1718, 1699 cmϪ1; FAB MS m/z 573
([M ϩ H]ϩ) (Calc. for C37H36N2O4: C, 77.60; H, 6.34; N, 4.89.
Found: C, 77.84; H, 6.39; N, 4.98%).
1 H), 8.07 (s, 2 H); IR (KBr) ν 1709, 1687 cmϪ1 (C᎐O); FAB MS
᎐
(m/z) 537 (Mϩ ϩ H, 28%), 536 (Mϩ, 30) (Calc. for C32H28-
N2O4S: C, 71.62; H, 5.25; N, 5.22. Found: C, 71.45; H, 5.30;
N, 5.04%).
3-(1-Butyl-3,3-dimethylindolin-2-ylidenemethyl)-3Ј-(1-butyl-1,4-
dihydroquinolin-4-ylidenemethyl)-4,4Ј-bi(cyclobut-3-ene-1,2-
dione) 2c
3-(2,3,6,7-Tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-
3Ј-(1-butyl-1,2-dihydroquinolin-2-ylidenemethyl)-4,4Ј-bis(cyclo-
1
1
but-3-ene-1,2-dione) 2i. Yield 30%; mp 320 ЊC (decomp.); H
Yield 50%; mp 274 ЊC; H NMR (270 MHz; CDCl3) δ 0.99 (t,
NMR (CDCl3) δ 1.10 (t, J = 7.3 Hz, 3 H), 1.52–1.88 (m, 2 H),
1.92–2.20 (m, 6 H), 2.81 (quint, J = 6.1 Hz, 4 H), 3.37 (t, J =
6.1 Hz, 4 H), 4.47 (t, J = 7.9 Hz, 2 H), 7.10 (s, vinyl H, 1 H),
7.39–7.70 (m, 4 H), 7.79 (d, J = 9.7 Hz, 2 H), 8.01 (s, 2 H),
J = 7.3 Hz, 3 H), 1.01 (t, J = 7.3 Hz, 3 H), 1.41–1.60 (m, 4 H),
1.72 (s, 6 H), 1.82–1.92 (m, 4 H), 4.15 (t, J = 7.3 Hz, 2 H), 4.24
(t, J = 7.3 Hz, 2 H), 7.02 (d, J = 7.3 Hz, 1 H), 7.15 (d, J = 7.3 Hz,
1 H), 7.29–7.37 (m, 3 H), 7.52–7.61 (m, 3 H), 7.74 (m, 1 H), 7.85
(s, 1 H), 8.47 (d, J = 7.3 Hz, 1 H), 8.64 (dd, J = 1.2 and 8.6 Hz,
1 H); IR (KBr) ν 1724, 1697 cmϪ1; FAB MS m/z 573 ([M ϩ H]ϩ)
(Calc. for C37H36N2O4: C, 77.60; H, 6.34; N, 4.89. Found:
C, 77.34; H, 6.31; N, 4.89%).
8.91 (d, J = 9.7 Hz, 1 H); IR (KBr) ν 1730, 1713 cmϪ1 (C᎐O);
᎐
FAB MS (m/z) 532 (Mϩ ϩ H, 26%), 531 (Mϩ, 43) (Calc. for
C34H30N2O4 ϩ 0.2H2O: C, 76.44; H, 5.74; N, 5.24%. Found: C,
76.38; H, 5.63; N, 5.28%).
X-Ray crystallographic analysis of 1a
3-[4-(Diethylamino)phenyl]-3Ј-(3-butyl-2,3-dihydrobenzo-
thiazol-2-ylidenemethyl)-4,4Ј-bis(cyclobut-3-ene-1,2-dione) 2d.
Yield 38%; mp 252 ЊC (decomp.); H NMR (CDCl3) δ 1.04 (t,
A single crystal of 1a suitable for X-ray crystallography was
obtained by recrystallization from a CH2Cl2 solution of 1a
in hexane by slow solvent diffusion. All reflection data were
collected on a Rigaku AFC5-R diffractometer using graphite-
monochromated Mo-Kα radiation. Intensity data were
collected in the range of 3 < 2θ < 55Њ using an ω–2θ scan
technique. The structure was solved by a direct method and
refined by a full matrix least-square procedure. The reflections
with I > 4σ(I ) were used for the structure refinement. All non-
hydrogen atoms, except C(9), were refined with anisotropic
thermal parameters. All hydrogen atoms were placed at the
calculated positions, and subsequently included in the structure
refinement. For the refinement, the TEXSAN program was
used. Tables of the atomic coordinates, isotropic thermal
parameters, full lists of bond lengths and angles, and least-
squares planes have been deposited in supplementary Tables.
Crystal data: C38H40N2O4, M 588.74, triclinic, space group
P-1, cell constants: a = 10.933(3), b = 17.941(5), c = 8.474(2) Å,
α = 92.31(3)Њ, β = 102.96(3)Њ, γ = 81.59(2)Њ, V = 1602.3(7) Å3, Z =
2, Dcalc = 1.220 g cmϪ3, unique reflections 4263, final R = 0.083,
Rw = 0.089.†
1
J = 7.3 Hz, 3 H), 1.45–1.64 (m, 2 H), 1.25 (t, J = 7.3 Hz, 6 H),
1.92 (quint, J = 7.3 Hz, 2 H), 3.50 (q, J = 7.3 Hz, 4 H), 4.31 (t,
J = 7.9 Hz, 2 H), 6.78 (t, J = 9.2 Hz, 2 H), 7.26–7.38 (m, 3 H),
7.49 (t, J = 7.9 Hz, 1 H), 7.68 (d, J = 7.9 Hz, 1 H), 8.46 (d, J = 9.2
Hz, 2 H); IR (KBr) ν 1738, 1733 cmϪ1 (C᎐O); FAB MS (m/z),
᎐
513 (Mϩ ϩ H, 100%), 512 (Mϩ, 69) (Calc. for C30H28N2O4S:
C, 70.29; H, 5.51; N, 5.46. Found: C, 69.99; H, 5.49; N, 5.30%).
3-[4-(Diethylamino)phenyl]-3Ј-(1-butyl-1,2-dihydroquinolin-2-
ylidenemethyl)-4,4Ј-bis(cyclobut-3-ene-1,2-dione) 2e. Yield 70%;
1
mp 248 ЊC (decomp.); H NMR (CDCl3) δ 1.10 (t, J = 7.3 Hz,
3 H), 1.25 (t, J = 7.3 Hz, 6 H), 1.70–1.99 (m, 4 H), 3.49 (q,
J = 7.3 Hz, 4 H), 4.48 (t, J = 7.9 Hz, 2 H), 6.77 (d, J = 9.2 Hz,
2 H), 7.09 (s, vinyl H, 1 H), 7.47 (t, J = 6.7 Hz, 1 H), 7.61–7.71
(m, 3 H), 7.82 (d, J = 9.2 Hz, 1 H), 8.40 (d, J = 9.2 Hz, 2 H), 8.91
(d, J = 9.2 Hz, 1 H); IR (KBr) ν 1738, 1732 cmϪ1 (C᎐O);
᎐
FAB MS (m/z) 507 (Mϩ ϩ H, 100%), 506 (Mϩ, 52) (Calc. for
C32H30N2O4: C, 75.86; H, 5.97; N, 5.53. Found: C, 74.94; H,
5.71; N, 5.43%).
3-[4-(Dibutylamino)phenyl]-3Ј-(3-butyl-2,3-dihydrobenzo-
thiazol-2-ylidenemethyl)-4,4Ј-bis(cyclobut-3-ene-1,2-dione) 2f.
Yield 33%; mp 257 ЊC (decomp.); 1H NMR (CDCl3) δ 1.86–0.06
† CCDC reference number 163768. See http://www.rsc.org/suppdata/
p1/b1/b104059f/ for crystallographic files in .cif or other electronic
format.
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830
2829

View Article Online
4 As a review, see: K.-Y. Law, Chem. Rev., 1993, 93, 449.
PPP MO calculations
5 (a) V. Y. Merritt and H. Hovel, J. Appl. Phys. Lett., 1976, 29, 414;
(b) D. L. Morel, K. Ghosh, T. Feng, E. L. Stogryn, P. E. Purwin,
R. F. Shaw and C. Fishman, J. Appl. Phys. Lett., 1978, 32,
495.
The PPP MO method was used with a valuable b approxim-
ation described in a previous paper.15 The standard ionization
potential and one-centre electron-repulsion integral for carbon
and oxygen atoms were used. For nitrogen atoms, Ip = 23.0 eV
and γrr = 17.44 eV were used. The simplest possible geometries
and planar structures were assumed for the molecules studied in
the PPP MO calculations.
6 As a review, see: H. Fabian, H. Nakazumi and M. Matsuoka, Chem.
Rev., 1992, 92, 1197.
7 M. Matsuoka, Absorption Spectra of Dyes for Diode Lasers (JOEM
Handbook vol. 2), eds. Y. Taniguchi, M. Irie, A. Yabe and
S. Watarai, Bunshin, Tokyo, 1990.
8 (a) W. Ziegenbein and H.-E. Sprenger, Angew. Chem., Int. Ed. Engl.,
1966, 5, 893; (b) H.-E. Sprenger and W. Ziegenbein, Angew. Chem.,
Int. Ed. Engl., 1966, 5, 894; (c) H.-E. Sprenger and W. Ziegenbein,
Angew. Chem., Int. Ed. Engl., 1967, 6, 553.
9 K.-Y. Law and F. C. Bailey, J. Org. Chem., 1992, 57, 3278.
10 E. Terpetschnig and J. R. Lakowicz, Dyes Pigm., 1993, 21,
227.
Acknowledgements
This work was supported by Tokyo Ohka Foundation for the
promotion of Science and Technology (1999) and by a Grant-
in-Aid for Scientific Research on Priority Areas (A) from the
Ministry of Education, Science, Sports, and Culture in Japan.
11 L. S. Liebeskind, M. S. Yu, R. H. Yu, J. Wang and K. S. Hagen,
J. Am. Chem. Soc., 1993, 115, 9048.
12 J. Fabian and H. Hartmann, Light Absorption of Organic Colorants
(Reactivity and Structure Concepts in Organic Chemistry vol. 12),
eds. K. Hafner, C. W. Rees, B. M. Trost, J.-M. Lehn, P. R. Schleyer
and R. Zahnradnik, Springer-Verlag, Berlin, 1980.
13 (a) K. Liang, M. S. Farahat, J. Perlstein, K.-Y. Law and D. G.
Whitten, J. Am. Chem. Soc., 1997, 119, 830; (b) H. Chen,
M. S. Farahat, K.-Y. Law and D. G. Whitten, J. Am. Chem. Soc.,
1996, 118, 2584; (c) P. V. Kamat, S. Das, K. G. Thomas and
M. V. George, J. Phys. Chem., 1992, 96, 195.
14 R. C. De Selm, C. J. Fox and R. C. Riordan, Tetrahedron Lett., 1970,
781.
15 S. Akiyama, S. Nakatsuji, K. Nakashima, M. Watanabe and
H. Nakazumi, J. Chem. Soc., Perkin Trans. 1, 1988, 3155.
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2830
J. Chem. Soc., Perkin Trans. 1, 2001, 2823–2830