Synthesis and colour spectrophotometric measurements of some novel merocyanine dyes

Article abstract of DOI:10.1016/j.dyepig.2011.03.019

Novel merocyanine dyes cyanine dyes derived from benzo[2,3-b; 2′, 3′ - b′ ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-, and pyra)-zine-6,12-dione ring system were prepared. The prepared cyanines involve acyclic merocyanine and cyclic merocyanine types. Colour sp

Full text of DOI:10.1016/j.dyepig.2011.03.019

Dyes and Pigments 92 (2012) 929e935
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Dyes and Pigments
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Synthesis and colour spectrophotometric measurements of some novel
merocyanine dyes
*
H.A. Shindy , M.A. El-Maghraby, Fayez M. Eissa
Department of Chemistry, Faculty of Science at Aswan, South Valley University, Aswan, Egypt
a r t i c l e i n f o
a b s t r a c t
Novel merocyanine dyes cyanine dyes derived from benzo[2,3-b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-,
thia-, and pyra)-zine-6,12-dione ring system were prepared. The prepared cyanines involve acyclic
merocyanine and cyclic merocyanine types. Colour spectrophotometric measurements for all the
synthesized merocyanine dyes were investigated in 95% ethanol solution. Colour spectrophotometric
measurements for some selected synthesized merocyanines were examined in pure solvents having
different polarities and/or in aqueous universal buffer solutions. General chemicalephysical character-
ization was carried out through elemental analysis, IR and 1H NMR spectral data.
Article history:
Received 19 January 2011
Received in revised form
12 March 2011
Accepted 15 March 2011
Available online 23 March 2011
Keywords:
Cyanine dyes
Ó 2011 Published by Elsevier Ltd.
Merocyanine dyes
Synthesis
Colour studies
Spectrophotometric measurements
1. Introduction
dyes, we prepared here some new solvatochromic and halochromic
merocyanine dyes as new synthesis contribution and spectroscopic
Cyanine dyes have been used for many years in various appli-
cations [1e16], such as silver halide sensitizers in photographic
industry, laser technology, immunoassays and flow cytometry, and
for labeling biomolecules for a variety of applications such as DNA
sequencing. Scientists favor using cyanine dyes in biological
applications because, among other reasons, many of the dyes
operate in the near IR (NIR) region of the spectrum (600e1000 nm).
This makes these cyanine dyes less susceptible to interference from
autofluorescence of biomolecules. Besides, merocyanine dyes have
practical application ranging from physics to medicine and biology
[17e20]; for example, they are extensively used as nonlinear optical
(LNO) materials, photosensitizers in the photodynamic treatment
of cancer, radiosensitizers in solid tumor treatment, diagnostic
agents in medicine and potentiometric sensors. Owing to their
pronounced solvatochromic effect, merocyanine dyes have found
widespread utilization as probes for solvent polarity [21]. In addi-
tion, merocyanine dyes are characterized by a large area of high-
tech applications, such as their application in procedures for
disinfection of blood products [22]. Taking in accounts and
consideration the above vital and important benefits of cyanine
investigation in this field, and/or to be used in any of the various
application fields of cyanine dyes, particularly as photographic
sensitizers, as indicators for solvent polarity and as indicators for
acidebase titration in analytical chemistry. Also, we hope that this
paper will be interesting, informative and stimulating not only for
cyanine dyes chemists, but also for scientists in other fields like
biochemistry, physics, pharmacology, medicine and for all whom
interested in the light absorbing systems in their research, labeling
biomolecules and/or in the synthesis and characterization of
complex organic compounds.
2. Results and discussion
2.1. Synthesis
Reaction of 4,10-diformyl-2,8-diphenyl-5,ll-dihydro-benzo[2,3-
b; 20, 30 - b0 ]bis pyrazolo [4,5-b]-l,4-(oxa-, thia-, and pyra-)zine
(1aec) [23] with equimolar (bimolar) ratios of acetone, acetylace-
tone, or ethylacetoacetate in ethanol as organic solvent containing
piperidine as a basic catalyst under refluxing conditions resulted
the acyclic merocyanine (bis-acyclic merocyanine) dyes 2aee
(3aee), Scheme 1, Table 1.
Chemical confirmation takes place for bis acyclic merocyanine
dyes 3aee, through the reactions of the acyclic merocyanine dyes
* Corresponding author.
E-mail address: hashindy@hotmail.com (H.A. Shindy).
0143-7208/$ e see front matter Ó 2011 Published by Elsevier Ltd.
doi:10.1016/j.dyepig.2011.03.019

930
H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
O
O
H
N
Ph
N
O
O
H
N
Ph
N
O
O
H
N
O
X
X
N
O
N
Me
N
H
N
N
R
OHC
N
H
X
N
OHC
N
H
X
N
Ph
Ph
(4a - c)
(2a - e)
O
N
N
O
O
O
N
N
H
R
N
Me
O
O
O
Ph
N
O
H
N
1 Mole
N
H
1 Mole
EtOH / pip.
X
CHO
R
EtOH / pip.
O
N
Me
N
1 Mole
EtOH / pip.
O
N
N
H
X
N
OHC
1 Mole
EtO H / pi p.
O
N
N
O
Ph
O
R
(1a - c)
Me
O
H
2 Mole
EtOH / pip.
2 Mole
EtOH / pip.
O
O
H
O
H
Ph
O
H
N
Ph
O
O
H
N
O
N
N
H
O
O
N
X
N
N
X
N
R
Me
N
N
O
N
Me
N
R
N
H
X
N
N
H
X
N
O
Ph
O
Ph
H
(3a - e)
(5a - C)
1a-c, 4a-c, 5a-c: a, X = O
b, X = S
2a-e; 3a-e: a, X = O, R = H
b, X = O, R = COCH
3
c, X = NH
c, X = O, R = COOEt
d, X = S, R = H
e, X = NH, R = H
Scheme 1.
2aee with equimolar ratios of the acetyl compounds (acetone,
acetylacetone, or ethylacetoacetate) in ethanol containing piperidine
to give the same bis acyclic merocyanine dyes 3aee obtained
via Route 1, characterized by the same melting points, mixed
melting points, same IR and 1H NMR spectral data, Route 2,
Scheme 1.
Additionally, reaction of equimolar (bimolar) ratios of barbitone
with the diformyl compounds 1aec in ethanol as organic solvent
Table 1
Characterization of the prepared compounds.
Comp. No.
Colour of crystals
Molecular Formula (M. Wt.)
M P ꢀC
Yield %
Analysis % (calcd/found)
Absorption Spectra in 95% Ethanol
C
H
N
lmax (nm)
3max (L moleꢁ1 cmꢁ1
)
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
4a
4b
4c
5a
5b
5c
Reddish brown
Bright violet
Reddish brown
Violet
C
29H18I2N6O6 (546.5)
190e192
195e197
187e189
201e203
209e211
203e205
202e204
167e169
213e215
215e217
188e190
207e209
200e202
197e199
211e213
209e211
39
71
77
68
63
59
68
78
74
78
39
42
51
71
83
82
63.74
63.70
63.27
63.32
62.14
62.11
60.20
60.22
63.97
64.00
65.53
65.55
64.47
64.46
62.46
62.48
62.12
62.09
65.75
65.77
58.45
58.39
55.55
55.56
58.63
58.60
56.20
56.19
53.82
53.80
56.36
56.34
3.32
3.29
3.43
3.44
3.58
3.60
3.14
3.17
3.70
3.68
3.78
3.76
3.91
3.88
4.14
4.13
3.58
3.60
4.14
4.17
2.62
2.66
2.49
2.51
2.95
2.93
2.50
2.47
2.39
2.35
2.78
2.77
15.38
15.39
14.28
14.30
13.59
13.59
14.52
14.50
20.58
20.55
14.33
14.39
12.53
12.55
11.50
11.47
13.58
13.60
19.17
19.19
18.18
18.21
17.28
17.29
22.79
22.83
19.28
19.30
18.46
18.42
23.20
23.16
447
13920
C31H20I2N6O6 (588.5)
C32H22I2N6O8 (618.6)
461
453
456
468
454
470
464
472
487
501
509
517
509.5
515
527
12710
12130
15610
15910
14110
16100
14910
15910
17010
17120
17820
18010
20010
19610
21310
C29H18N6O4S2 (578.6)
Pale violet
Reddish brown
Bright violet
Reddish brown
Violet
C29H20N8O4 (544.5)
C32H22N6O6 (586.6)
C36H26N6O6 (670.6)
C38H30N6O10 (730.7)
C32H22N6O4S2 (618.7)
C32H24N8O4 (584.6)
C30H16N8O8 (616.5)
Pale violet
Violet
Bright violet
Intense violet
Violet
C30H16N8O6S2 (648.6)
C30H18N10O6 (614.5)
C34H18N10O10 (726.6)
C34H18N10O8S2 (758.7)
Pale violet
Intense violet
C34H20N12O8 (724.6)

H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
931
Table 2
Colour spectrophotometric measurements for the merocyanine dyes (3b); (5a) in pure solvents.
Solvent H2O
EtOH
DMF
CHCl3
CCl4
Dioxane
Dye
No.
lmax 3max
(nm) (L moleꢁ1 cmꢁ1
lmax
3max
lmax 3max
(nm) (L moleꢁ1 cmꢁ1
lmax 3max
(nm) (L moleꢁ1 cmꢁ1
lmax 3max
(nm) (L moleꢁ1 cmꢁ1
lmax 3max
(nm) (L moleꢁ1 cmꢁ1
)
)
(nm) (L moleꢁ1 cmꢁ1
)
)
)
)
(3b)
467
e
12530
e
470
e
16100
e
437
491
527
13220
16840
21120
422
475
518
11440
10720
15050
425
481
520
12980
10590
12310
429
484
524
12530
10280
11060
(5a)
505
16940
509.5 20010
containing piperidine as a basic catalyst under refluxing conditions
achieved the cyclic merocyanine (bis cyclic merocyanine) dyes
4aec (5aec), Scheme 1, Table 1.
Chemical confirmation is obtained for the bis cyclic mer-
ocyanine dyes 5aec through the reactions of the cyclic mer-
ocyanine dyes 4aec with equimolar ratios of barbitone in ethanol
containing piperidine to give the same bis cyclic merocyanine dyes
5aec obtained via Route 1, characterized by the same melting
points, mixed melting points, same IR and 1H NMR spectral data,
Route 2, Scheme 1.
carbon, which enhances the electronic charge transfer, and the role
of electron accepting groups which minimize the electronic charge
transfer pathways inside the dye molecule. Also, it was observed
that the oxazine dyes 2a (3a) gives hypsochromic shifted bands
accompanied with decreasing the intensity of the bands if
compared with the thiazine and pyrazine dyes 2d,2e (3d,3e). This
can be due to the more electron attracting character of the oxazine
ring compared with thiazine and pyrazine rings, Scheme 1, Table 1.
Besides, it is noticed that, the electronic visible absorption spectra
of bis-acyclic merocyanine dyes (3aee) disclose bathochromic
shifted and intensified bands if compared with their analogous
acyclic merocyanine dyes (2aec), Scheme 1, Table 1. This is due to
the increase of the number of electronic charge transfer pathways
in the bis-acyclic merocyanine dyes 3aee, if compared with their
analogous acyclic merocyanine dyes 2aee, Scheme 2 (A), Table 1.
Additionally, it was found that the electronic visible absorption
spectra bands and their molar extinction coefficients of the cyclic
merocyanine (bis cyclic merocyanine) dyes 4aec (5aec) in 95%
ethanol showed bathochromic and/or hypsochromic shifted bands
with increase and/or decrease of the intensities of these bands,
depending on the nature of the six membered heterocyclic nuclei
and the number of the electronic charge transfer pathways inside
the dye molecule, Schemes 1, 2 (B), Table 1. This can be related to
the same reasons cited before in the case of the acyclic (bis-acyclic)
merocyanine dyes 2aee (3aee).
The structure of the prepared compounds was determined by
elemental analysis, (Table 1), IR [24] and 1H NMR [25] spectroscopy,
Table 4.
2.2. Colour spectrophotometric measurements
2.2.1. a - In 95% ethanol solution
Colour spectrophotometric measurements for all the prepared
merocyanine dyes were made by measuring their electronic visible
absorption spectra in 95% ethanol solution. The dyes are thought to
be deeper in colour when they absorb light at longer wavelength
(bathochromic shifted and/or red shifted dyes), and consequently
the lightining of the dye colour increase when they absorb light at
shorter wavelength (hypsochromic shifted and/or blue shifted
dyes). So, we may say that the colour of one dye is deeper than the
other one if the wavelength of the maximum of absorption spec-
trum of the former is longer than that of the latter one [26].
The acyclic merocyanine dyes (bis-acyclic merocyanine dyes)
2aee (3aee) showed and disclosed electronic absorption spectra in
95% ethanol in visible region 447e468 nm (454e487 nm) where
their band positions and molar extinction coefficients are largely
affected by both the nature of the side group (R), the benzbihe-
terocyclic ring system present in the dye molecule, and the number
of electronic charge transfer pathways inside the dye molecule,
Table 1, Scheme 1. Thus, substituting R ¼ H in dyes 2a (3a) by
R ¼ ꢁCOCH3, -COOEt to obtain dyes 2b,2c (3b,3c), respectively,
causes bathochromic shifts for the spectral absorption bands,
Table 1, Scheme 1. This can be related to the presence of additional
carbonyl groups in the latter dyes, which leads to additional elec-
tronic charge transfer pathways inside the dye molecules. In
addition, substituting the methyl group in dyes 2b (3b) by the
ethoxy group to obtain dyes 2c (3c) resulted blue shifted absorption
bands with decreasing the intensities of these bands Table 1,
Scheme 1. This can be attributed to the electron accepting character
of the ethoxy group in dyes 2c (3c) and the electron releasing
character of the methyl group in dyes 2b (3b). This clearly declare
the role of the electron donating groups replaced on the carbonyl
2.2.2. b - In pure solvents having different polarities
Colour spectrophotometric measurements for some selected
synthesized merocyanine dyes were made by measuring their
electronic visible absorption spectra in pure solvents having
different polarities. The dyes tend to give deeper colours and/or
longer wavelength bands (bathochromic shifted and/or red shifted
bands) in the solvents which have higher polarity and/or dielectric
constants. So, we can say that, this solvent is more polar than the
other one when the wavelength of the maximum of the absorption
spectra bands of the dye in the former solvent is longer than in the
latter one. Inversely, the dyes tend to give lighter colours and/or
shorter wavelength bands (hypsochromic shifted and/or blue
shifted bands) in the solvents which have lower polarity and/or
dielectric constants. So we can say that this solvent is less polar
than the other one when the wavelength of the maximum of the
absorption spectra bands of the dye in the former solvent is shorter
than in the latter one. Therefore, these cyanine dyes can be used as
indicators for solvent polarity [27]. Deviation from this rule occurs
when there are specific solvent interaction between the dye
and solvent, like hydrogen bonding and/or molecular complex
formation.
Table 3
The variation of absorbance with pH at fixed
l for the merocyanine dyes (3b); (5a) in different buffer solution.
pH
Dye
1.87
0.900
1.275
2.51
0.932
1.306
3.92
1.180
1.423
5.06
1.280
1.617
6.89
1.360
1.755
8.13
1.550
1.947
9.56
1.700
2.009
11.41
1.730
2.074
pKa
4.240; 8.235
8.655
Absorbance at settled wavelength
(3b)
(5a)
l
l
470 (nm)
505 (nm)

932
H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
Table 4
[29]. These charge transfers are due to transfer of an electron lone
IR and 1HNMR spectral data of the prepared dyes.
pair from the N-Ph pyrazole nitrogen atom to the positively charged
carbon atom of the carbonyl group, Scheme 2 (A), (B).
The data given in Table 2 show that the charge transfer band
exhibits a hypsochromic shift in ethanol relative to DMF, dioxane,
chloroform and carbontetrachloride. This effect may be attributed
to the following factors :
Dye IR cmꢁ1
1H NMR (DMSO)
d Assignment
2b
3b
4a
5a
631,696 (-Ph);
1369 (CeN);
4.28 (s, 6H, 2CH3, 2COCH3);
5.98 (s, 2H, 2NH);
1678 (C]O quinone); 6.84e7.98 (m, 11H, aromatic & CH ¼ );
1758 (C]O);
3313 (NH cyclic).
679,770 (-Ph);
1371 (CeN);
9.23 (s, 1H, CHO).
4.27 (s, 12H, 4CH3, 4COCH3);
5.86 (s, 2H, 2NH);
a. The bathochromic shift in DMF relative to ethanol is a result of
the increase in solvent polarity due to the increase of dielectric
constant of DMF relative to ethanol.
b. The hypsochromic shift occurring in ethanol relative to dioxan,
chloroform and carbontetrachloride is a result of the solute
solvent interaction through intermolecular hydrogen bond
formation between ethanol and the lone pair electrons of N-Ph
pyrazole nitrogen atom, Scheme 3 (A). This slightly decreases
the electron density on the N-Ph pyrazole nitrogen atom, and
consequently decreases to some extent the mobility of the
1691 (C]O quinone); 6.80e8.12 (m, 12H, aromatic & 2CH ¼ ).
1731 (C]O);
3281 (NH cyclic).
641,717 (-Ph);
5.80 (s, 2H, 2NH);
1300,1375 (CeN);
1681 (C]O quinone); 9.36 (s, 1H, CHO).
1733 (C]O);
6.54e8.57 (m, 13H, aromatic & 2CH ¼ );
3401 (NH cyclic).
633,682 (-Ph);
5.98 (s, 2H, 2NH);
1323, 1361 (CeN);
1692 (C]O quinone);
1748 (C]O);
6.52e8.42 (m, 16H, aromatic & 2CH ¼ & 4NH).
attached
p electrons over the conjugated pathway to the
3424 (NH cyclic).
positively charged carbon atom of the carbonyl group.
Also, from Table 2, it was observed the occurrence of unexpected
hypsochromic shift with decreasing the intensity in the lmax of the
longer wavelength in water relative to ethanol. This can be mainly
ascribed to the possible interaction of water molecules with the
lone pair electrons of N-Ph pyrazole nitrogen atom, Scheme 3 (A).
This makes difficult the charge transfer to the positively charged
carbon atom of the carbonyl group, and consequently a hyp-
sochromic shift is observed in water relative to ethanol.
The electronic visible absorption spectra of the bis acyclic
merocyanine dye (3b) and bis cyclic merocyanine dye (5a) in pure
solvents of different dielectric constant viz water (78.54), DMF
(36.70), ethanol (24.3), chloroform (4.806), carbontetrachloride
(2.238) and dioxane (2.209) [28] are recorded. The lmax and 3max
values of the absorption bands due to different electronic transi-
tions within the solute molecule in these solvents are represented
in Table 2, Fig. 1 (A).
From Table 2 it is clear that, the electronic visible absorption
spectra of the dyes (3b), (5a) in ethanolic medium are characterized
by the presence of one or two essential absorption bands. These
bands can be assigned to intramolecular charge transfer transitions
2.2.3. c - In aqueous universal buffer solutions
Colour spectrophotometric measurements for some selected
synthesized merocyanine dyes were examined by measuring their
electronic visible absorption spectra in aqueous universal buffer
Ph
N
O
O
O
Ph
N
O
O
O
H
N
H
N
X
X
N
Me
N
Me
R
N
N
R
OHC
N
H
X
N
OHC
N
H
X
N
Ph
Ph
(2a - e)
A
Ph
N
O
O
Ph
N
O
O
O
H
N
H
N
X
X
N
Me
N
Me
R
R
R
N
N
Me
Me
R
N
H
X
N
N
H
X
N
O
Ph
Ph
O
O
(3a - e)
O
O
Ph
N
O
O
Ph
O
H
N
H
N
H
N
H
N
X
N
X
N
O
N
O
N
H
N
H
N
N
N
OHC
N
H
X
OHC
N
H
X
N
O
O
Ph
O
Ph
(4a - c)
B
O
Ph
O
H
N
H
N
O
O
N
X
H
N
O
N
O
O
Ph
O
O
H
N
H
N
N
H
O
N
O
O
N
X
H
N
N
H
X
N
O
N
O
N
H
N
H
O
Ph
N
(5a - c)
N
H
X
N
O
N
H
Ph
Scheme 2.

H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
933
Fig. 1.
solutions. The dyes tend to give deeper colours and/or longer
wavelength bands (bathochromic shifted and/or red shifted bands)
in the buffer solutions having higher pH media and/or basic media.
So, we can say that this buffer solution is more basic than the other
one when the wavelength of the maximum of the absorption
spectra bands of the dye in the former buffer is longer than in the
latter one. Inversely, the dyes tend to give lighter colours and/or
shorter wavelength bands (hypsochromic shifted and/or blue
shifted bands) in the buffer solutions having lower pH media and/
or acidic media. So, we can say that this buffer solution is more
acidic than the other one when the wavelength of the maximum of
the absorption spectra bands of the dye in the former buffer is
shorter than in the latter one. Therefore, these cyanine dyes can be
used as indicators for the pH of the buffer solutions and/or as
indicators in acidebase titrations in analytical chemistry [30].
The solutions of the bis acyclic merocyanine dye (3b) and bis
cyclic merocyanine dye (5a) have a permanent cationic charge in
basic media which then discharged on acidification. This prompted
and encouraged us to study their spectral behaviour in different
buffer solutions in order to select a suitable pH for the use of these
dyes as photosensitizers. The acid dissociation or protonation
constant of these dyes have been determined. The effect of the
compounds as photosensitizers increase when they are present in
the ionic form, which has a higher planarity [31], and therefore
more conjugation.
The electronic absorption spectra of the bis acyclic merocyanine
dye (3b) and bis cyclic merocyanine dye (5a) in aqueous universal
buffer solutions of varying pH values (1.87, 2.51, 3.92, 5.06, 6.89,
8.13, 9.56 and 11.41) showed bathochromic shifts with intensifica-
tion of their absorption bands at high pH (alkaline media) and
X
X
O
O
H
Ph
O
H
Ph
O
O
O
H
N
O
H
N
H
O
O
N
O
O
N
O
H
N
N
O
Me
N
Me
N
O
A
N
H
Me
N
H
O
N
H
N
H
O
N
Me
N
H
O
N
N
H
O
O
O
Ph
Ph
O
X
O
X
(5a)
(3b)
X = C2H5 (in ethanol); H (in water)
O
O
H
Ph
H
O
H
N
H
Ph
O
H
O
O
N
O
O
H
N
N
O
N
O
O
Me
N
O
N
N
Me
B
N
H
O
N
H
N
H
O
N
Me
N
N
H
N
H
O
N
Me
O
Ph
O
O
Ph
H
(5a)
(3b)
Scheme 3.

934
H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
hypsochromic shifts with quenching the intensity of the bands at
low pH media (acidic media), Table 3, Fig. 1 (B). So, the mentioned
dyes which have an electrons lone pair of on the N-ph pyrazole
nitrogen atom undergoes to protonation in low pH (acidic media).
This leads to a criterion of positive charge on N-Ph pyrazole
nitrogen atom, and consequently the electronic charge transfer
pathways to the positively charged carbon atom of the carbonyl
group will be difficult resulting in a hypsochromic shift for the
absorption band, Scheme 3 (B). On increasing the pH of the media,
the absorption bands are intensified and bathochromically shifted
due to deprotonation of the N-Ph pyrazole nitrogen atom, and
consequently the electronic charge transfer pathways to the posi-
tively charged carbon atom of the carbonyl group will be easier and
facilitated, Scheme 3 (B).
Several methods have been developed for spectrophotometric
determination of the dissociation constants of weak acids. The
variation of absorbance with pH can be utilized. On plotting the
absorbance at the lmax vs. pH, S-shaped curves are obtained, Fig. 1
(B), Table 3.
In all of the S-shaped curves obtained, the horizontal portion to
the left corresponds to the acidic form of the indicator, while the
upper portion to the right corresponds to the basic form, since the
pKa is defined as the pH value for which one half of the indicator is
in the basic form and the other half in the acidic form. This point is
determined by intersection of the curve with a horizontal line
midway between left and right segments [32]. The acid dissociation
or protonation constants values of the dyes are summarized in
Table 3.
3.2. Synthesis
3.2.1. Synthesis of 3,9-diethyl-4,10-diformyl-2,8-diphenyl-5,11-
dihydro-benzo[2,3-b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-,
andpyra-)zine 1aec
The synthesis of compounds 6aec was carried out as in the
reported procedure [23].
3.2.2. Synthesis of 3,9-diethyt-(l0-formyl)-2,8-diphenyl-5,ll-
dihydro-benzo[2,3-b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-,
and pyra-)zine-4-acyclic merocyanine 2aee
A mixtures of equimolar ratios (0.01 mol) of {acetone, acetyla-
cetone, or ethylacetoacetate} and bis formyl compounds 1aec were
refluxed for 8 h in ethanol (100 ml) as organic solvent containing
piperidine (1 ml) as basic catalyst. The reaction mixture, which
changed from brown to deep brown during the reaction, was filtered
while hot to remove unreacted material, concentrated, cooled,
neutralized with glacial acetic acid and precipitated by adding cold
water. The acyclic merocyanine dyes 2aee were dried, collected and
crystallized from ethanol. The relevant data are given in Table 1.
3.2.3. Synthesis of 3,9-diethyt-2,8-diphenyl-5,ll-dihydro-benzo[2,3-
b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-, and pyra-)zine-
4,10-bis acyclic merocyanine dyes 3ae
Two different routes were used to synthesize these cyanine
dyes.
3.2.3.1. Route (1). 1 : 2 M ratios of the bis formyl compounds 1aec
and (acetone, acetylacetone, or ethylacetoacetate) were heated
under reflux for 8 h in ethanol (100 ml) containing piperidine
(1 ml). The reaction mixture, which changed from brown to deep
brown during the refluxing conditions was filtered while hot to
remove unreacted materials, concentrated, cooled, neutralized
with glacial acetic acid and precipitated by adding cold water. The
bis acyclic merocyanine dyes 3aee were dried, collected and crys-
tallized from ethanol. The relevant data are given in Table 1.
2.3. Conclusion
From the results discussed in this study we can conclude that
due to the spectral and/or the photosensitization properties of
these cyanine dyes, they can be used and/or employed as photo-
graphic sensitizers for silver halide emulsions in photographic
industry because they can increase the sensitivity range of the
photographic emulsions by making an increase in the range of
wavelength which form an image on the film. In addition, these
cyanine dyes can be used as indicators for solvent polarity due to
their solvatochromic properties. Besides, these cyanine dyes can be
used as acidebase indicators in analytical chemistry. This is because
these dyes have halochromic properties, where they gives
a reversible colour change as a result of a change in the pH. Hal-
ochromic compounds are acids or bases in which a change in the
pH causes a change in the ratio of ionized and non ionized states, as
these two states have different colours, the colour of the solution
changes (rewords). This colour change can be used in acid-base
titrations in analytical chemistry, where the colour change of the
halochrome corresponds to the end-point of the reaction.
3.2.3.2. Route (2). Piperidine (1e2 ml) was added to a mixture of
equimolar ratios (0.01 mol) of 2aec and (acetone, acetylacetone or
ethylacetoacetate} dissolved in ethanol. The reaction mixture was
heated under refluxfor8handattainedadeepbrowncolourattheend
of refluxing. It was filtered while hot, concentrated, cooled, neutralized
by glacial acetic acid and precipitated by adding cold water. The
precipitated products were filtered of, washed several times with
water, dried and crystallized from ethanol to give the compounds
obtained through Route (1), characterized by melting points, mixed
melting points, same IR and 1H NMR spectra data, Tables 1, 4, Scheme 1.
3.2.4. Synthesis of 3,9-diethyl-10-formyl-2,8-diphenyl-5,11-
dihydro-benzo[2,3-b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-,
and pyra-)zine-4-cyclic merocyanine 4aec
3. Experimental
Barbitone (0.01 mol) were heated under reflux with equimolar
ratios of the diformyl compound 1aec in ethanol (100 ml) as
organic solvent and piperidine (1 ml) as a basic catalyst for 6 h. At
the end of the reflux, the reaction mixture was filtered off on hot,
concentrated, neutralized with glacial acetic acid and precipitated
by adding ice-water mixture. The separated cyclic merocyanine
dyes 4aec were filtered, washed with water, and crystallized from
ethanol. The results are listed in Table 1.
3.1. General
All the prepared compounds were purified using chromato-
graphic techniques (Column chromatography). Melting points were
measured using Galenkamp melting point apparatus and are
uncorrected. Elemental analyses were carried out at the Microan-
alytical Center at Cairo University by an automatic analyzer (Her-
aeus). IR (KBr pellets) spectra were determined in 1650 FT-IR
instrument (Cairo University), and the 1H NMR spectra were
accomplished using 300 MHz NMR Spectrometer (Cairo Univer-
sity). Electronic visible absorption spectra were carried out on
Shimadzu UVeVisible recording spectrometer (South Valley
University, Faculty of Science at Aswan).
3.2.5. Synthesis of 3,9-diethyl-2,8-diphenyl-5,11-dihydro-benzo
[2,3-b; 20, 30 - b0 ]bis pyrazolo[4,5-b]-l,4-(oxa-, thia-, and pyra-)
zine-4,10-bis cyclic merocyanine dyes 5aec
These cyanine dyes were prepared by the following two
different routes.

H.A. Shindy et al. / Dyes and Pigments 92 (2012) 929e935
935
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3.2.5.1. Route (1). Barbitone (0.02 mol) and diformyl compounds
1aec (0.01 mol) were dissolved in ethanol (100 ml), and then
piperidine (1 ml) was added. The reaction mixture was refluxed for
6 h. At the end of the reflux, the reaction mixture was filtered off on
hot, concentrated, neutralized with glacial acetic acid and precipi-
tated by adding ice-water mixture. The separated bis cyclic mer-
ocyanine 5aec were filtered, washed with water, and crystallized
from ethanol. The results are listed in Table 1.
3.2.5.2. Route (2). Equimolar ratios (0.01 mol) of barbitone and the
previously prepared cyclic merocyanine dyes 4aec were dissolved
in ethanol (100 ml) containing piperidine (1 ml). The reaction
mixture was heated under reflux for 6 h and attained a deep
permanent colour at the end of refluxing. It was filtered while hot,
concentrated and cooled. The precipitated products obtained after
addition of cold water, were filtered of, washed with water,
collected and crystallized from ethanol to give the same bis-cyclic
merocyanine dyes 5aec obtained by Route (1), characterized by
melting points, mixed melting points, same IR and 1H NMR spectral
data, Tables 1, 4, Scheme 1.
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