Synthesis, spectroscopic characterization and photophysical study of dicyanomethylene-substituted squaraine dyes

Article abstract of DOI:10.1016/j.crci.2012.01.009

In this work, the synthesis and the photophysical study of novel symmetrical and unsymmetrical squaraine dyes is described. These dyes were prepared by base-catalyzed condensation reaction between 3H-indolium or benzothiazolium salts with dicyanomethylene squarate, derived from squaric acid. The photophysical behavior of the dyes was investigated using UV-Vis absorption and steady-state fluorescence in solution. Additionally, its association with albumin from bovine serum (bovine serum albumin [BSA]) was also investigated. The dyes present strong absorption in the red/infrared regions and fluorescence emission in the infrared region tailored by the electronic structure of the squaraine. Association experiments with bovine serum albumin indicate that the obtained squaraine dyes are suitable for protein detection in solution.

Full text of DOI:10.1016/j.crci.2012.01.009

C. R. Chimie 15 (2012) 454–462
Contents lists available at SciVerse ScienceDirect
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Full paper/M e´ moire
Synthesis, spectroscopic characterization and photophysical study
of dicyanomethylene-substituted squaraine dyes
a,
b
a
Diego dos Santos Pisoni *, Cesar Liberato Petzhold , Marluza Pereira de Abreu ,
a
a
Fabiano Severo Rodembusch , Leandra Franciscato Campo
a
Universidade Federal do Rio Grande do Sul. Instituto de Qu ı´ mica, Laborat o´ rio de Novos Materiais Org aˆ nicos, Avenida Bento Gon c¸ alves,
500, CP 15003, CEP 91501-970, Porto Alegre-RS, Brazil
9
b
Universidade Federal do Rio Grande do Sul. Instituto de Qu ı´ mica, Laborat o´ rio de S ı´ ntese Org aˆ nica e Pol ı´ meros, Avenida Bento Gon c¸ alves,
500, CP 15003, CEP 91501-970, Porto Alegre-RS, Brazil
9
A R T I C L E I N F O
A B S T R A C T
Article history:
In this work, the synthesis and the photophysical study of novel symmetrical and
unsymmetrical squaraine dyes is described. These dyes were prepared by base-catalyzed
condensation reaction between 3H-indolium or benzothiazolium salts with dicyano-
methylene squarate, derived from squaric acid. The photophysical behavior of the dyes
was investigated using UV–Vis absorption and steady-state fluorescence in solution.
Additionally, its association with albumin from bovine serum (bovine serum albumin
Received 25 November 2011
Accepted after revision 23 January 2012
Available online 28 February 2012
Keywords:
Fluorescence
Proteins
[
BSA]) was also investigated. The dyes present strong absorption in the red/infrared
regions and fluorescence emission in the infrared region tailored by the electronic
structure of the squaraine. Association experiments with bovine serum albumin indicate
that the obtained squaraine dyes are suitable for protein detection in solution.
ß 2012 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Sensors
Heterocycles
Conjugation
Squaraine dyes
1
. Introduction
Squaraines are a class of strongly colored dyes bearing a
labels in biological assay [18] due their unique physico-
chemical and photophysical properties namely light
absorption in the visible red and near-infrared regions
[19].
Squaraine dyes are generally prepared by the conden-
sation of electron rich aromatic, heteroaromatic or olefinic
compounds with squaric acid or its esters in a one-step
reaction [20]. In a typical procedure, symmetrical squa-
raines 3 are synthesized by the reaction of dialkyl esters
derived from squaric acid, e.g. 3,4-dibutoxy-3-cyclobu-
tene-1,2-dione 1 with two equivalents of a quaternized
methylene base, e.g. 1,3,3-trimethyl-2-methyleneindoline
2 (Scheme 1) [21].
central electron deficient four-membered ring core sur-
rounded by electron rich aromatic moieties. These dyes are
interesting compounds in chemical synthesis mainly
because their species show strong absorption bands
5
À1
À1
(
e ꢀ 10 L.mol .cm ) in the visible region [1], intense
fluorescence emission [2] and good photoconductivity [3].
These features make them useful in a variety of applica-
tions in the area of imaging [4,5], nonlinear optics [6–8],
photodynamic therapy [9–12], photovoltaic devices [13–
1
5], ion sensing [16], as well as in organic synthesis [17].
Furthermore, squaraine dyes are suitable for fluorescence
detection of proteins at long-wavelength excitation and
Unsymmetrical squaraines are synthesized via a multi-
step procedure (Scheme 2) [22]. In the first step, the
reaction of squaric ester 1 with an equimolar amount of
heterocyclic quaternary ammonium salt 2, in the presence
of triethylamine as catalyst and n-butanol as solvent,
leads to the intermediate mono-squaraine 4. Subsequent
reaction of 4 with a second equimolar amount of a
*
Corresponding author.
E-mail addresses: diego_qui@yahoo.com.br (D.d.S. Pisoni),
campo@iq.ufrgs.br (L.F. Campo).
1
631-0748/$ – see front matter ß 2012 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2012.01.009

D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
455
Scheme 1.
Scheme 2.
methylene base affords the corresponding unsymmetrical
squaraine 6.
Although similar structures have been presented in the
2. Results and discussion
2.1. Synthesis of squaraine dyes
literature, this work presents the synthesis of new
dicyanomethylene-substituted squaraine dyes with good
yields and fluorescence emission in infrared region.
Additionally, we believe that this manuscript can contri-
bute not only in the field of fluorescence sensors, but as
well as new dyes with potential application as dye
sensitized solar cells [23,24].
Symmetrical dicyanomethylene-substituted squaraine
dye 11 was synthesized in four steps from squaric acid as
shown in Scheme 3. The synthetic route includes initially
the reaction of squaric acid (7) and excess of n-butanol to
afford the dibutyl ester 1 [25], which was subsequently
treated with 1.0 equivalent of malononitrile in the
Scheme 3.

4
56
D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
idine mixture [28], afforded the symmetrical dye 11 in
9% yield.
3
The synthesis of the unsymmetrical squaraine dye 16
was performed as depicted in Scheme 4. In the first step, 2-
aminothiophenol (12) was treated with 1.0 equivalent of
acetyl chloride at room temperature using toluene as
solvent to afford 2-methylbenzothiazole (13) in 85% yield
after purification by chromatography [29]. Subsequent
quaternization of 13 using excess of iodooctane led to the
N-octyl-2-methylbenzothiazolium iodide (14) in satisfac-
tory yield (68% after purification). Condensation of 1.0
equivalent of 10 with 1.0 equivalent of squarate 8, in the
presence of triethylamine and ethanol as solvent, afforded
the intermediate mono-squaraine 15 [30]. Reflux of crude
product containing mainly 15 with benzothiazolium salt
10 in an n-butanol:benzene mixture led to the unsymme-
trical dye 16 in 25% yield from quaternized indolenine 10.
The squaraine dye 17 was obtained in 42% yield in a
unique step by condensation of 1.0 equivalent of the 3-
dicyanomethylene squarate 8 with 2.0 equivalents of
benzothiazolium 14 under reflux in an n-butanol:pyridine
mixture (Scheme 5).
2.2. Photophysical characterization of free dyes in organic
solvents
In Figs. 1–3 are presented the normalized UV–Vis
absorption and fluorescence emission spectra of the
squaraine dyes 11, 16 and 17 in 1,4-dioxane, chloroform,
ethanol, dimethylformamide and dimethylsulfoxide. The
spectral shapes of the dyes are almost the same as
expected [31], and the relevant data are summarized in
Table 1.
An absorption band maxima located around 681, 687
and 702 nm, with high molar extinction coefficient values
Scheme 4.
(
e
) in agreement with
pÀp* transitions, could be observed
in the squaraines 11, 16 and 17, respectively. It can also be
seen that the electronic structure plays a fundamental role
in the absorption spectra of the squaraine dyes. The
symmetrical indolium derivative 11 presents the lower
absorption maxima in all studied solvents despite of the
dyes 16 and 17, which present a bathochromic absorption,
indicating more delocalized electronic structure due to the
sulfur atom in the dye structure. For all dyes studied, a
small solvatochromic effect could be observed (13–16 nm)
in the non-protic environments, which can be due to
solvent effects determined by the electronic polarizability
presence of triethylamine to give triethylammonium-2-
butoxy-3-dicyanomethylene-4-oxocyclobut-1-en-1-olate
(8) in 85% yield [26]. Next, commercially available 2,3,3-
trimethylindol (9) was converted in the heterocyclic
quaternary ammonium salt 10 by coupling of 9 with
excess of iodooctane (5.0 equiv.) in 75% yield after
chromatography [27]. The subsequent base-catalyzed
condensation of 2.0 equivalents of 3H-indolium salt 10
and 1.0 equivalent of 8 under reflux in an n-butanol:pyr-
Scheme 5.

D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
457
Fig. 1. Normalized absorption and fluorescence emission spectra of the squaraine dye 11.
Fig. 2. Normalized absorption and fluorescence emission spectra of the squaraine dye 16.

4
58
D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
Fig. 3. Normalized absorption and fluorescence emission spectra of the squaraine dye 17.
of the solvent and the molecular polarizability resulting
from reorientation of solvent dipoles. The latter property is
a function of the static dielectric constant, e. However, the
structure was also observed in the excited state in despite
of the absorption data. Concerning similar structures
presented in the literature, the dyes 11 and 16 presented
ethanol (to dye 11), dimethylformamide and dimethylsulf-
oxide (to dyes 16 and 17) present a blue-shifted band in
relation to the other solvents, which probably indicates
that specific interactions are produced by one or a few
neighboring molecules, and are determined by the specific
chemical properties of both the fluorophore and solvent,
such as hydrogen bonding or preferential solvation [32].
The curves of fluorescence were obtained using the
absorption maxima as the excitation wavelengths. One
main emission band located around 694, 703 and 717 nm
could be observed in the squaraines 11, 16 and 17,
respectively, where no aggregation in the studied organic
solvents was detected [31]. The similar solvatochromic
effect and the red shift depending on the electronic
higher quantum yields in all studied solvents (
fl
F = 0.19 to
dye 11 and = 0.17 to dye 16, Table 1). The excitation
F
fl
spectra were also obtained and are quite similar to the UV–
Vis absorption spectra, which indicate that no significative
conformational or electronic changes took place in the
excited state (Figs. S20–S22, Supporting information).
2.3. Photophysical characterization of free dyes in buffer
Proteins can be covalently or non-covalently labeled
with different fluorophores. The latter is applied in some
biochemical and biomedical applications for investigations
of conformational changes in proteins or determination of
drug-binding constants [18]. In this way, several works
Table 1
Relevant photophysical data from UV–Vis absorption and fluorescence emission of the squaraine dyes 11, 16 and 17.
 10 (MÀ1ÁcmÀ1
5
)
lem (nm)
l
ex (nm)
À1
Stokes’ shift (nm/cm )
F
fl
Dye
Solvent
l
abs (nm)
e
11
16
17
1,4-Dioxane
689
685
673
681
1.90
0.99
0.73
1.94
702
695
687
691
686
686
671
681
13/321
10/247
14/345
10/247
0.19
0.18
0.13
0.08
CHCl
3
EtOH
DMF
1,4-Dioxane
694
690
681
681
1.46
1.42
6.52
1.39
709
709
699
702
691
688
681
683
15/370
19/462
18/438
21/511
0.16
0.17
0.15
0.16
CHCl
DMF
3
DMSO
1,4-Dioxane
709
704
696
696
1.61
1.78
1.28
1.37
723
724
711
717
710
688
688
688
14/340
20/487
15/365
21/511
0.09
0.13
0.14
0.14
CHCl
DMF
3
DMSO

D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
459
Fig. 4. Fluorescence spectra of 2
different concentrations of bovine serum albumin (BSA) in pH = 7.0 (0,
.02, 0.04, 0.06, 0.14, 0.20, 0.80 and 1.0 M BSA) at room temperature.
mM squaraine dye 11 associated with
Fig. 6. Fluorescence spectra of 2
m
M squaraine dye 17 associated with
different concentrations of bovine serum albumin (BSA) in pH = 7.0 (0,
.04, 0.06, 0.10, 0.12, 0.16, 0.20, 0.60 and 1.0 BSA) at room
0
m
0
mM
temperature.
Table 2
have been suggesting that squaraine dyes can occupy
common hydrophobic binding sites on the protein to form
stable conjugates, which can enhance the squaraine
fluorescence emission and be used for the protein
determination [31,33]. Herein, the spectral properties of
squaraines 11, 16 and 17 upon binding to bovine serum
albumin (BSA) as a model protein were investigated. The
fluorescence spectra of squaraine dyes associated with
different concentration of BSA are shown in Figs. 4–6. In
the absence of BSA, it was observed that the squaraine
dyes are almost nonfluorescent. On the other hand, the
fluorescence intensity increases by addition of BSA in the
Relevant photophysical data of the squaraine dyes 8, 13 and 14 in
phosphate buffer solution (PBS) buffer.
In bovine serum
albumin (BSA)
absence
In bovine serum albumin (BSA)
a
presence
BSA
BSA
BSA
Dye
lem (nm)
I
f
(a.u.)
lem (nm)
I
f
(a.u.)
f f
I /I
11
689
689
696
13
13
27
697
698
707
463
634
167
36
49
6
1
1
6
7
l
em: maximum wavelength of fluorescence emission of the squaraine
dye; I : emission intensity of dye in free state. The excitation/emission
slits were kept constant for each dye.
f
phosphate buffer solution (PBS)/squaraine dye solution
a
BSA concentration of 1 mM.
BSA
(
f f
I /I ) by a factor from 6 up to 49 (Table 2). An additional
emission band could be observed, located at 750 nm in low
BSA content. It is well known that the self-association of
dyes in solution is a usual phenomenon in dye chemistry
owing to strong intermolecular van der Waals-like
attractive forces between the molecules, such as cyanines
and squaraines [34], which allows fluorescence emission
with spectral shifts when compared to the monomeric
species. However, a red shift emission band located at the
same position could be detected to the PBS solution
without the squaraine dyes (control solution). In this way,
we are not able to attribute this emission band as being due
to the squaraine dye aggregates in solution.
3. Conclusions
In summary, we have successfully synthesized new
symmetrical and unsymmetrical squaraine dyes based on
indolium and benzothiazolium moieties. Symmetrical
squaraine dyes 11 and 17 were prepared by base-catalyzed
condensation reaction between 2.0 equivalents of 3H-
indolium or benzothiazolium salts, respectively, with 1.0
equivalent of dicyanomethylene squarate 8, derived from
squaric acid (7). Unsymmetrical squaraine dye 16 was
prepared in two steps via mono-squaraine intermediate
15, obtained from condensation reaction between 1.0
equivalent of 3H-indolium salt 10 and 1.0 equivalent of
dicyanomethylene squarate 8. The dyes presented strong
absorption and fluorescence emission between 680 nm
Fig. 5. Fluorescence spectra of 2
different concentrations of bovine serum albumin (BSA) in pH = 7.0
0, 0.02, 0.04, 0.06, 0.10, 0.12, 0.16, 0.20, 0.40 and 1.0 M BSA) at room
temperature.
mM squaraine dye 16 associated with
and 724 nm with high molar extinction coefficient values
(
m
5
(
e
> 10 ) and fluorescence quantum yields between 0.08

4
60
D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
and 0.19. In addition, no aggregation could be observed in
solution of organic solvents. Additionally, the squaraines
displayed a considerable increase in fluorescence emission
by a factor of up 6 to 49 in the presence of albumin from
bovine serum.
stirred at room temperature for 20 min. The solvent was
removed under reduced pressure to afford the dicyano-
methylene 8, which was used without any further
purication in the next step. The spectroscopic data of 8
( H NMR and C NMR) were in agreement with those
reported previously in literature [26].
1
13
4
. Experimental
4.1.3. 1-Octyl-2,3,3-trimethyl-3H-indolium iodide (10)
4.1. General
A mixture of 1-iodooctane (1.2 g, 5.0 mmol) and 2,3,3-
trimethylindol (9) (0.16 g, 1.0 mmol) was heated at 145 8C
during 3 h. After cooling, the resultant mixture was
purified by column chromatography using silica gel and
1
13
H and C NMR spectra were recorded on a Varian
Inova 300 MHz spectrometer. The chemical shifts are
expressed as (ppm) relative to tetramethylsilane as an
d
2 2
CH Cl :MeOH as eluent mixture (8:2) to give 0.2 g
internal standard and J standard values are given in Hz. IR
spectra were measured on a Mattson Galaxy Series FT-IR
(0.75 mmol, 75% yield) of 1-octyl-2,3,3-trimethyl-3H-
1
indolium iodide (10). The spectroscopic data of 10 ( H
1
3
3
000 (model 3020). The UV–Vis absorption and fluores-
cence emission spectra were obtained on a Shimadzu UV-
450 spectrophotometer and a Shimadzu RF-5301PC
NMR and C NMR) were in agreement with those reported
previously in literature [37].
2
spectrofluorometer, respectively. Spectroscopic grade sol-
vents (Merck or Aldrich) were used in fluorescence
emission and UV–Vis absorption spectroscopy measure-
4.1.4. Squaraine dye (11)
A mixture of 8 (233 mg, 0.73 mmol) and 10 (400 mg,
1.46 mmol) was refluxed in 16 mL of an n-butanol:pyridine
mixture (1:1, v/v) for 12 h. The solvent was removed under
reduced pressure and the residue was purified by column
chromatography using silica gel and CHCl
eluent mixture (95:5) to afford 191 mg (0.29 mmol, 39%
ments. The quantum yield of fluorescence (
fl
F ) was
measured at 25 8C in spectroscopic grade solvents with a
solution with absorbance intensity lower than 0.05. Zinc
phthalocyanine (ZnPc) was synthesized according to the
literature [35] and used as quantum yield standard
3
:ethyl acetate as
1
3
yield) of dye 11 as green solid; H NMR (300 MHz, CDCl ) d
(
F
fl
= 0.20 in dimethylsulfoxide [DMSO]) [36]. Purication
7.36 (4H, m), 7.20 (2H, t, J = 7.2 Hz), 7.06 (2H, d, J = 8.1 Hz),
6.53 (2H, s), 4.02 (4H, t, J = 7.2 Hz), 1.79 (4H, m), 1.78 (12H,
by column chromatography was carried out on silica gel 60
1
3
(
(
70–230 mesh). Analytical thin-layer chromatography
TLC) was conducted on Merck aluminum plates with
m), 1.46 (4H, m), 1.27 (20H, m), 0.87 (6H, t, J = 6.9 Hz);
C
NMR (75 MHz, CDCl 173.3, 171.9, 167.9, 166.7, 142.6,
3
) d
0
1
.2 mm of silica gel 60F-254. 3,4-dibutoxycyclobut-3-ene-
,2-dione (1), triethylammonium-2-butoxy-3-dicyano-
142.2, 128.2, 124.7, 122.4, 119.2, 110.3, 89.3, 49.5, 44.6,
31.9, 29.5, 29.3, 27.5, 26.9, 26.8, 22.8, 14.3; IR (KBr) 2925,
2855, 2193, 1492, 1454, 1359, 1285, 1111 cm ; Analysis:
À1
methylene-4-oxocyclobut-1-en-1-olate (8), 1-octyl-2,3,3-
trimethyl-3H-indolium iodide (10), 2-methylbenzothia-
zole (13) and N-octyl-2-methylbenzothiazolium iodide
56 4
Calcd. for C45H N O: C, 80.80; H, 8.44; N, 8.38. Found: C,
80.75; H, 8.40; N, 8.36.
(
14) were prepared according to the procedures described
in this work. Squaric acid (7), 2,3,3-trimethylindol (9),
-aminothiophenol (12), 1-iodooctane, malononitrile,
4.1.5. 2-Methylbenzothiazole (13)
2
To a solution of 2-aminothiophenol (12), (0.31 g,
phthalonitrile, zinc acetate and nitrobenzene were pur-
chased from Sigma Aldrich and used without purification.
BSA fraction V was purchased from Alamar Tecno-
Cient ı´ fica LTDA.
2.5 mmol) in 2.5 mL of toluene was added dropwise
0.18 mL of acetyl chloride (0.2 g, 2.5 mmol). The mixture
was kept under stirring at room temperature during
25 minutes. Next, the mixture was diluted with ethyl
3
acetate (10 mL) and sat. aq. NaHCO (5 mL). The organic
4.1.1. 3,4-Dibutoxycyclobut-3-ene-1,2-dione (1)
layer was separated and the aqueous layer extracted with
In a 100 mL round bottom flask with reflux condenser, a
ethyl acetate (3 Â 5 mL). The combined extracts were
mixture of squaric acid (7) (1.0 g, 8.77 mmol) and dry n-
butanol (30 mL) was heated at reflux for 24 h using a Dean
Stark trap. After solvent removal under reduced pressure,
the product was purified by column chromatography using
silica gel and hexane:ethyl acetate as eluent mixture (8:2)
to give 1.39 g (6.17 mmol, 70% yield) of 3,4-dibutoxycy-
washed with H
2
O (3 Â 5 mL), dried (Na
2 4
SO ) and concen-
trated under reduced pressure. The crude product was
purified by column chromatography using silica gel and
hexane:ethyl acetate as eluent mixture (8:2) to give 0.32 g
(2.12 mmol, 85% yield) of 2-methylbenzothiazole (13). The
1
13
spectroscopic data of 13 ( H NMR and C NMR) were in
1
clobut-3-ene-1,2-dione (1). The spectroscopic data of 1 ( H
agreement with those reported previously in literature [29].
13
NMR and C NMR) were in agreement with those reported
previously in literature [25].
4.1.6. N-Octyl-2-methylbenzothiazolium iodide (14)
A mixture of 1-iodooctane (1.2 g, 5.0 mmol) and 2-
methylbenzothiazole (13) (0.15 g, 1 mmol) was heated at
145 8C during 3 h. After cooling, the resultant mixture was
purified by column chromatography using silica gel and
4
.1.2. Triethylammonium-2-butoxy-3-dicyanomethylene-4-
oxocyclobut-1-en-1-olate (8)
To a solution of 3,4-dibutoxycyclobut-3-ene-1,2-dione
(
1
1) (320 mg, 1.42 mmol) and malononitrile (92 mg,
.39 mmol) in 6.0 mL of benzene was added, dropwise
with stirring, 0.19 mL of triethylamine. The mixture was
2 2
CH Cl :MeOH as eluent mixture (8:2) to give 0.18 g
(0.68 mmol, 68% yield) of N-octyl-2-methylbenzothiazo-
1
lium iodide (14). The spectroscopic data of 14 ( H NMR and

D.S. Pisoni et al. / C. R. Chimie 15 (2012) 454–462
461
1
3
C
NMR) were in agreement with those reported
agreement with the literature
em = 678 nm in DMSO) [35].
(
l
abs = 673 nm and
previously in literature [37].
l
4.1.7. Mono-squaraine (15)
4.3. Bovine serum albumin association
A solution of 8 (229 mg, 0.72 mmol) and 10 (0.15 g,
0
.55 mmol) in 2 mL of EtOH, in presence of 0.1 mL of Et
3
N,
Different BSA concentrations (BSA fraction V) were
labeled with the squaraine dyes in a concentration of
was heated at 70 8C for 1 h. After removal of solvent, the
crude product containing mainly the mono-squaraine 15
was used in the next step without further purification.
2
mM. In a previous solution of the dyes, in PBS, was added
different volumes of BSA solution, also in PBS. The final
solution was gentle stirred for 1 h. The fluorescence
spectra were recorded with increasing the BSA concen-
tration until concentration where the fluorescence
intensity saturates.
4.1.8. Unsymmetrical squaraine dye (16)
A mixture of 14 (204 mg, 0.77 mmol) and mono-
squaraine 15 (400 mg, 0.77 mmol) was refluxed in 30 mL
of n-butanol:benzene mixture (1:1, v/v) for 18 h using
Dean-Stark trap. The solvent was removed under reduced
pressure and the residue was purified by column
Acknowledgements
3
chromatography using silica gel and CHCl :ethyl acetate
The authors thank the Conselho Nacional de Desenvol-
vimento Cient ı´ fico e Tecnol o´ gico (CNPq) and the Instituto
Nacional de Inova c¸ a˜ o em Diagn o´ sticos para Sa u´ de P u´ blica
as eluent mixture (8:2) to afford 91 mg (0.14 mmol, 25%
1
yield from 10) of dye 16 as green solid; H NMR (300 MHz,
CDCl
3
)
d
7.64 (1H, d, J = 7.8 Hz), 7.49 (1H, t, J = 8.4 Hz), 7.32
4H, m), 7.15 (1H, t, J = 7.5 Hz), 6.99 (1H, d, J = 7.8 Hz), 6.54
1H, s), 6.31 (1H, s), 4.21 (2H, t, J = 7.2 Hz), 3.94 (2H, t,
(
INDI-Sa u´ de) for financial support.
(
(
Appendix A. Supplementary data
J = 7.2 Hz), 1.78 (4H, m), 1.75 (6H, m), 1.42 (4H, m), 1.27
13
(
3
16H, m), 0.87 (6H, t, J = 6.9 Hz); C NMR (75 MHz, CDCl ) d
1
1
1
2
2
74.0, 169.8, 166.4, 165.4, 163.6, 162.3, 142.5, 142.2, 140.8,
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.crci.2012.01.009.
28.8, 128.0, 127.9, 125.4, 123.8, 122.7, 122.3, 119.2, 118.9,
12.7, 109.6, 48.9, 47.4, 44.2, 41.1, 31.9, 31.9, 29.6, 29.4,
9.3, 29.2, 27.9, 27.3, 27.1, 26.9, 22.8, 22.7, 14.3; IR (KBr)
References
À1
925, 2854, 2192, 1506, 1457, 1268, 1115 cm ; Analysis:
[1] S. Sreejith, P. Carol, P. Chithra, A. Ajayaghosh, J. Mater. Chem. 18 (2008)
Calcd. for C42
50 4
H N OS: C, 76.55; H, 7.65; N, 8.50. Found: C,
264.
7
6.03; H, 7.85; N, 8.12.
[
[
[
[
[
2] S.H. Kim, J.H. Kim, J.Z. Cui, Y.S. Gal, S.H. Jin, K. Koh, Dyes Pigm. 55 (2002) 1.
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1
mixture (1:1, v/v) for 12 h. The solvent was removed under
reduced pressure and the residue was purified by column
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chromatography using silica gel and CHCl
3
:ethyl acetate
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as eluent mixture (9:1) to afford 208 mg (0.32 mmol, 42%
1
3
yield) of dye 17 as dark solid; H NMR (300 MHz, CDCl ) d
7
6
.55 (2H, d, J = 7.8 Hz), 7.41 (2H, t, J = 7.8), 7.24 (4H, m),
.25 (2H, s), 4.11 (4H, t, J = 7.2 Hz), 1.82 (4H, m), 1.46 (4H,
[
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1
3
m), 1.27 (16H, m), 0.87 (6H, t, J = 6.9 Hz);
C NMR
(
75 MHz, CDCl
3
)
d
174.2, 163.9, 162.6, 160.6, 141.0, 128.5,
[
1
2
1
C
6
27.6, 124.7, 122.4, 118.9, 112.1, 87.0, 47.0, 31.9, 29.4,
[
9.2, 27.7, 27.0, 22.7, 14.2; IR (KBr) 2926, 2852, 2185,
À1
456, 1434, 1257, 1154, 1130 cm ; Analysis: Calcd. for
[
39
H
44
N
4
OS
2
: C, 72.18; H, 6.83; N, 8.63. Found: C, 73.19; H,
[
[
[
.58; N, 8.45.
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(
[
[
[
20] A.H. Schmidt, Synthesis (1980) 961.
A mixture of phthalonitrile (4.3 g, 33 mmol) and zinc
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acetate (2.5 g, 114 mmol) in nitrobenzene was refluxed
during 5 h. After cooling, the resulting mixture was filtered
and washed with ethanol and acetone to give a violet
powder. Next, the solid was purified by Soxhlet extraction
with toluene, ethanol and acetone. The resulting solid was
treated with hot aqueous solution of 10% aq. HCl and
subsequently hot aqueous solution of 10% aq. NaOH to give
[
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Acta Cryst. E60 (2004) o2252.
4
,0 g (83% yield) of ZnPc. The expected structure is in
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4
62
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[
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[
[
[
[
29] S. Rudrawar, A. Kondaskar, A.K. Chakraborti, Synthesis 15 (2005) 2521.
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[
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