Thermally stable water insoluble azo-azomethine dyes: Synthesis, characterization and solvatochromic properties

Article abstract of DOI:10.1016/j.saa.2012.07.013

Six new water insoluble azo-azomethine dyes have been synthesized via condensation reaction of α,α′-bis(o-aminophenylthio)-1,2- xylene with substituted azo-coupled salicylaldehyde. The condensation reaction provides the expected bis-iminated azo-azomethin

Full text of DOI:10.1016/j.saa.2012.07.013

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Thermally stable water insoluble azo-azomethine dyes: Synthesis,
characterization and solvatochromic properties
⇑
Hamid Khanmohammadi , Khatereh Rezaeian
Department of Chemistry, Faculty of Science, Arak University, Arak 38156-8-8349, Iran
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
New thermally stable bis-iminated water insoluble azo-azomethine dyes were synthesized via conden-
"
"
"
New bisiminated water insoluble
azo-azomethine dyes have
synthesized.
Solvatochromic properties of the
dyes in various organic solvents has
been investigated.
sation reaction of a,
a0-bis(o-aminophenylthio)-1,2-xylene with substituted azo-coupled salicylaldehyde.
The effect of various organic solvents with different polarities on the UV–Vis spectra of the dyes has been
investigated.
Thermal behavior of the prepared
dyes has been reported.
a r t i c l e i n f o
a b s t r a c t
Six new water insoluble azo-azomethine dyes have been synthesized via condensation reaction of a, -
a0
Article history:
Received 22 April 2012
Received in revised form 10 June 2012
Accepted 5 July 2012
bis(o-aminophenylthio)-1,2-xylene with substituted azo-coupled salicylaldehyde. The condensation
reaction provides the expected bis-iminated azo-azomethine dyes in good yields, ranging from 59% to
90%. The dyes have been characterized by IR, UV–Vis and 1H NMR spectroscopic methods as well as ele-
mental analysis. The thermal behavior of the prepared dyes has been determined using thermogravime-
try technique. Furthermore, the effect of various organic solvents with different polarities on the UV–Vis
spectra of the dyes has been also studied.
Available online 16 July 2012
Keywords:
Azo-azomethine
Dye
Ó 2012 Elsevier B.V. All rights reserved.
Solvatochromism
Substitution effect
Thermal properties
Substituent effects
Introduction
used as dyestuffs for wool, leather and synthetic fabrics because
of their extraordinary coloring properties and in photonic devices
During the past decade, considerable attention has been paid to
the synthesis of azo dyes [1–3]. Azo dyes have been extensively
and components of optical communication systems because of
their second order nonlinear optical properties [4–8]. The spectral
properties of azo dyes depend on the nature of both the azo and the
coupling components. Among such coupling dyes, those containing
azo and azomethine groups are capable of exhibiting some inter-
esting structural properties and uses [9–13].
⇑
Corresponding author. Tel.: +98 861 2777401; fax: +98 861 4173406.
E-mail address: h-khanmohammadi@araku.ac.ir (H. Khanmohammadi).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.013

H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
653
Furthermore, considerable attentions have been paid to the
Experimental
study of azo-azomethine dyes containing hydroxyl groups in
recent years [14–16]. Intermolecular proton transfer of this class
of dyes has important consequences on their electronic structure
which can be exploited for their thermochromic and/or photochro-
mic behavior [17] and also design of molecular electronic devices
[18]. It is well known that polyhydroxy derivatives of azo-azome-
thine dyes show a self-isomerization induced by an intermolecular
and/or intramolecular proton transfer, which occurs from the
hydroxyl oxygen to either imine or azo nitrogen, respectively, in
both cases through intramolecular OAHꢀ ꢀ ꢀN hydrogen bonds
[14,15,19,20]. Also, the tautomerism in polyhydroxy derivatives
of azo-azomethine dyes is very attractive from practical viewpoint
and has been of particular interest [21–23]. The presence of azo/
imino, phenol/imino and hydrazone/azo-enaminone tautomerism
in these compounds may influence considerably on their unique
photo-physical and photo-chemical properties, which is in turn
strongly influenced by several factors including temperature, the
substituent structure and solvent polarity [24]. The solvent-depen-
dent tautomerism is closely related to the nature and degree of
dye–solvent interactions and can arise from either non-specific
or specific solute–solvent interactions [25].
Materials
All of the reagents and solvents involved in synthesis were of
analytically grade and used as received without further purifica-
tion. Salycilaldehyde, 4-nitroaniline, 4-chloroaniline, 4-ethylani-
line, 4-methylaniline, 4-bromaniline and 4-flouroaniline were
obtained from Aldrich and Merck.
a,
a0-bis(o-aminophenylthio)-
1,2-xylene, a, was prepared according to the literature procedure
[27]. Azo-coupled salicylaldehyde precursors, 1–3, were prepared
according to the well-known literature procedure [16,26].
Instrumentation
The structure of all synthesized compounds was confirmed by
1H NMR spectra, recorded on a Bruker AV 300 MHz spectrometer.
FT-IR spectra were recorded as pressed KBr discs, using Unicom
Galaxy Series FT-IR 5000 spectrophotometer in the region of
400–4000 cmꢁ1. Melting points were determined on Electrother-
mal 9200 apparatus. Thermal analyses were performed on a TGA
V5.1 A DuPont 2000 and Perkin-Elmer Thermogravimetric Ana-
lyzer TG/DTA 6300 instruments. C. H. N. analyses were performed
on a Vario EL III elemental analyzer. Electronic spectral measure-
ments were carried out using Perkin-Elmer Lambda spectropho-
tometer in the range 200–700 nm.
According to the spectroscopic properties of reported azo-azo-
methine compounds, our interest has been focused on preparation
of new o-hydroxy azo–azomethine derivatives with various donor
and acceptor groups [26]. We report here synthesis and character-
ization of new acyclic azo-azomethines, 1a–6a (Fig. 1), by conden-
sation reaction of azo-coupled salicylaldehyde derivatives, 1–6,
with a,
a0-bis(o-aminophenylthio)-1,2-xylene, a, [27]. All prepared
multifunctional compounds are air stable solids, intensely colored,
Synthesis
soluble in DMF and DMSO and exhibited dye characteristics since
General procedure for the synthesis of azo-coupled precursors, 4–6
Salicylaldehyde (10 mmol) was dissolved in water (20 mL) con-
taining 10 mmol of sodium hydroxide and 40 mmol of sodium car-
bonate during a period of 30 min at 0 °C. The resulting solution was
added slowly to a solution of diazonium chloride (10 mmol) in
water at 0–5 °C. The reaction mixture was stirred for 1 h at 0 °C
and then allowed to warm slowly to room temperature. The prod-
uct was collected by filtration and washed with 100 mL of NaCl
the molar extinction coefficients (e
) were over 30,000 Mꢁ1 cmꢁ1
[28]. The solvatochromic behavior and substituent effect of the
potentially polydentate prepared compounds in various solvents
were also evaluated. In addition, the thermal properties of the pre-
pared dyes were examined by thermogravimetric analysis. The
results indicated that the framework of the prepared dyes is stable
up to 295 °C.
H
O
+
R
N
N
OH
H2N
S
S
NH2
a
1
2
3
4
5
6
4-NO2 4-Et 4-Cl 4-Br 4-F 4-Me
R
N
S
S
N
H
H
R
N
N
OH
HO
N
N
R
1a-6a
Fig. 1. Synthesized azo-azomethine dyes.

654
H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
solution (10%) under vacuum. The obtained solid was dried under
(CAO), 1065, 833. Anal. Calcd. for C46H34N6O2S2Cl2: C, 65.94; N,
vacuum at 80 °C overnight.
10.03; H, 4.09; S, 7.65. Found: C, 65.73; N, 10.35; H, 4.22; S,
7.76%. kmax (nm) (
e
(Mꢁ1 cmꢁ1)): 268 (30738), 354(49604) in
1-(3-Formyl-4-hydroxyphenylazo)-4-bromobenzene, 4. Yield: 91%,
m.p. = 206–207 °C. 1H NMR (d6-DMSO, 300 MHz, ppm): d 7.19 (d,
1H, J = 8.86 Hz), 7.78 (br, s, 4H), 8.09 (dd, 1H, J = 8.86 Hz and
2.41 Hz), 8.18 (d, 1H, J = 2.41 Hz), 10.36 (s, 1H), 11.61 (br, 1H). IR
(KBr, cmꢁ1); 1668 (CHO), 1620 (C@C), 1572 (phenol ring), 1475
(N@N), 1286 (CAO), 1167, 829 and 719.
DMSO.
1,2-bis(4-((4-bromophenyl)diazenyl)-2-((2-(methylthio)phenylimino)
methyl)phenol)methylenbenzene, 4a. Yield; 62%, m.p. = 176–178 °C.
1H NMR (d6-DMSO, 300 MHz, ppm) dH: 4.36 (s, 4H), 7.07 (d, 2H,
J = 8.92 Hz), 7.21 (m, 2H), 7.31 (m, 6H), 7.47 (m, 4H), 7.76 (br,
8H), 7.96 (dd, 2H, J = 8.92 Hz and 2.30 Hz), 8.20 (d, 2H,
J = 2.30 Hz), 9.02 (s, 2H), 13.77 (br, 2H). IR (KBr, cmꢁ1); 1614
(C@N), 1574 (phenol ring), 1472 (N@N), 1350, 1285 (CAO), 1188,
1065, 831. Anal. Calcd. for C46H34N6O2S2Br2: C, 59.62; N, 9.07; H,
3.70; S, 6.92. Found: C, 59.83; N, 9.34; H3.97; S, 6.71%. kmax (nm)
1-(3-Formyl-4-hydroxyphenylazo)-4-flourobenzene, 5. Yield: 93%,
m.p. = 156–158 °C. 1H NMR (d6-DMSO, 300 MHz, ppm): d 7.17 (d,
1H, J = 8.76 Hz), 7.37 (br, t, 2H), 7.88 (m, 2H), 8.04 (dd, 1H,
J = 8.76 and 2.22 Hz), 8.14 (d, 1H, J = 2.22 Hz), 10.35 (s, 1H), 11.48
(br, 1H). IR (KBr, cmꢁ1); 1672 (CHO), 1620 (C@C), 1595 (phenol
ring), 1574, 1501, 1479 (N@N), 1287 (CAO), 1226, 1152, 839, 767.
(e
(Mꢁ1 cmꢁ1)): 256 (36945), 359 (38602), 450 (12313) in DMSO.
1,2-bis(4-((4-flourophenyl)diazenyl)-2-((2-(methylthio)phenylimi-
no)methyl)phenol)methylenbenzene, 5a. Yield; 59%, m.p. = 119–
120 °C. 1H NMR (d6-DMSO, 300 MHz, ppm) dH: 4.37 (s, 4H), 7.31
(m, 18H), 7.90 (s, 6H), 8.20 (s, 2H), 9.04 (s, 2H), 13.73 (br, 2H). IR
(KBr, cmꢁ1); 1614 (C@N), 1593 (phenol ring), 1579, 1498, 1472
(N@N), 1352, 1285 (CAO), 1223, 1107, 1065, 843. Anal. Calcd. for
1-(3-Formyl-4-hydroxyphenylazo)-4-methylbenzene, 6. Yield: 95%,
m.p. = 142–144 °C. 1H NMR (d6-DMSO, 300 MHz, ppm): d 3.80(s,
3H), 6.31 (d, 1H, J = 9.64 Hz), 7.02 (d, 2H, J = 9.64 Hz), 7.66 (d, 2H,
J = 8.75 Hz), 7.69 (dd, 1H, J = 9.64 and 2.73 Hz), 7.82 (d, 1H,
J = 2.73 Hz), 10.01 (s, 1H). IR (KBr, cmꢁ1); 1668 (CHO), 1620
(C@C), 1576 (phenol ring), 1481 (N@N), 1287 (CAO), 1174, 817,
739.
C46H34N6O2S2F2: C, 68.64; N, 10.44; H, 4.26; S, 7.97. Found: C,
68.43; N, 10.76; H, 4.37; S, 8.19%. kmax (nm) (e
(Mꢁ1 cmꢁ1)): 261
(40352) and 349(55898) in DMSO.
General procedure for the synthesis of azo-azomethine dyes, 1a–6a
A solution of diamine, a, (1 mmol) in absolute EtOH (10 mL) was
added to a stirring solution of azo-coupled precursors, 1–6,
(2 mmol) in absolute EtOH (50 mL) during a period of 10 min at
60–70 °C. The mixture was heated in water bath for 4 h at 80 °C
with stirring. The mixture was filtered whilst hot and the obtained
solid was washed with hot ethanol (three times) and then with
diethyl ether. The resulted product was dried in air.
1,2-bis(4-((4-methylphenyl)diazenyl)-2-((2-(methylthio)phenylimi-
no)methyl)phenol)methylenbenzene, 6a. Yield; 82%, m.p. = 127–
130 °C. 1H NMR (d6-DMSO, 300 MHz, ppm) dH: 2.39 (s, 6H), 4.38
(s, 4H), 7.08 (d, 2H, J = 8.87 Hz), 7.22 (m, 4H), 7.34 (m, 8H), 7.48
(m, 4H), 7.75 (d, 4H, J = 8.12 Hz) 7.95 (d, 2H, J = 8.78 Hz), 8.19 (s,
2H), 9.04 (s, 2H), 13.68 (br, 2H). IR (KBr, cmꢁ1); 1612 (C@N),
1580 (phenol ring), 1579, 1497, 1470 (N@N), 1352, 1283 (CAO),
1155, 1105, 824, 754. Anal. Calcd. for C48H40N6O2S2: C, 72.34; N,
10.54; H, 5.06; S, 8.05. Found: C, 72.63; N, 10.84; H, 4.91; S,
1,2-bis(4-((4-nitrophenyl)diazenyl)-2-((2-(methylthio)phenylimi-
no)methyl)phenol)methylenbenzene, 1a. Yield; 65%, m.p. = 240–
242 °C. 1H NMR (d6-DMSO, 300 MHz, ppm) dH: 4.36 (s, 4H), 7.05
(d, 2H, J = 9.11 Hz), 7.22 (m, 2H), 7.31 (m, 6H), 7.48 (m, 4H), 7.96
(d, 4H, J = 8.44 Hz), 7.99 (s, 2H), 8.21 (s, 2H), 8.35 (d, 4H,
J = 8.44 Hz), 9.02 (s, 2H), 13.94 (br, 2H). IR (KBr, cmꢁ1); 1616
(C@N), 1524 (NO2), 1580 (phenol ring), 1472 (N@N), 1344 (NO2),
1288 (CAO), 1105, 860. Anal. Calcd. for C46H34N8O6S2: C, 64.32;
N, 13.05; H, 3.99; S, 7.47. Found: C, 64.87; N, 13.41; H, 4.32; S,
8.23%. kmax (nm) (e
(Mꢁ1 cmꢁ1)): 274 (37332) and 353(58065) in
DMSO.
Result and discussion
New water insoluble azo-azomethine compounds, 1a–6a, have
been synthesized via condensation reaction of 5-(4-X-phenyl)-
azo-salicyladehyde (X = NO2, Et, Cl, Br, F and Me) with a,
a0-bis(o-
7.30%. kmax (nm) (e
(Mꢁ1 cmꢁ1)): 256 (50494), 374 (59973), 533
aminophenylthio)-1,2-xylene, a, in ethanol which were easily
identified by their IR and 1H NMR spectra. All the prepared multi-
functional Schiff bases are thermally stable up to 295 °C, air stable
solids, intensely colored and are soluble in DMF and DMSO, Table 1.
The entire new Schiff bases seemed to have dye characteristics be-
cause of their extraordinary coloring properties and their high mo-
lar extinction coefficient [29]. The existence of AN@NA and
AC@NA moieties in structure of the prepared dyes has caused
them to show specific spectral properties. Also, the presence of
N2S2O2 donor set of atoms makes the prepared dyes as very versa-
tile species, which could potentially act as multidentate ligands.
(18890) in DMSO.
1,2-bis(4-((4-ethylphenyl)diazenyl)-2-((2-(methylthio)phenylimi-
no)methyl)phenol)methylenbenzene, 2a. Yield; 90%, m.p. = 142–
145 °C. 1H NMR (d6-DMSO, 400 MHz, ppm) dH: 1.22 (t, 6H,
J = 7.60 Hz), 2.69 (q, 4H, J = 7.60 Hz), 4.38 (s, 4H), 7.08 (d, 2H,
J = 8.80 Hz), 7.21 (m, 2H), 7.32 (m, 6H), 7.40 (d, 4H, J = 8.40 Hz),
7.48 (m, 4H), 7.78 (d, 4H, J = 8.40 Hz), 7.95 (dd, 2H, J = 8.80 Hz,
J = 2.80 Hz), 8.20 (d, 2H, J = 2.80 Hz), 9.04 (s, 2H), 13.68 (br, 2H).
IR (KBr, cmꢁ1); 1612 (C@N), 1612 (C@C), 1580 (phenol ring),
1470 (N@N), 1283 (CAO), 1107, 839. Anal. Calcd. for C50H44N6O2S2:
C, 72.79; N, 10.19; H, 5.38; S, 7.77. Found: C, 73.04; N, 10.32; H,
5.61; S, 7.64%. kmax (nm) (e
(Mꢁ1 cmꢁ1)): 269(40623), 352(62564)
in DMSO.
Table 1
Azo-azomethine dyes, 1a–6a.
1,2-bis(4-((4-chlorophenyl)diazenyl)-2-((2-(methylthio)phenylimi-
no)methyl)phenol)methylenbenzene, 3a. Yield: 64%, m.p. = 181–
184 °C. 1H NMR (d6-DMSO, 300 MHz, ppm) dH: 4.37 (s, 4H), 7.07
(d, 2H, J = 8.86 Hz), 7.21 (m, 2H), 7.31 (m, 6H), 7.47 (m, 4H), 7.62
(d, 4H, J = 8.61 Hz), 7.84 (d, 4H, J = 8.61 Hz), 7.95 (d, 2H,
J = 8.86 Hz), 8.19 (s, 2H), 9.03(s, 2H), 13.76 (br, 2H). IR (KBr,
cmꢁ1); 1616 (C@N), 1578 (phenol ring), 1470 (N@N), 1352, 1285
Products
R
m.p. (°C)
Yeild (%)
1a
2a
3a
4a
5a
6a
4-NO2
4-CH2CH3
4-Cl
4-Br
4-F
240–242
142–145
181–184
176–178
119–120
127–130
65
90
64
62
59
82
4-Me

H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
655
Infrared spectra
show a major loss of weight where the corresponding DTA curves
show an exothermic peak. The exothermic peak indicates decom-
position of the azo dyes backbone. The comparison of Td (decompo-
sition temperature) showed that the thermal stability of the azo
dyes increases in the order 1a > 3a ꢂ 2a > 6a > 4a ꢂ 5a (Table 3).
This fact should be related with structure of the dyes and indicates
that the full conjugated 4-nitro substituted dye, 1a, is thermally
more stable than the others. Above 400 °C, the TG curves of all dyes
show continuous significant weight loss up to 900 °C, Fig. 2.
The position of some of the prominent bands in the IR spectra of
1–6 and 1a–6a and their assignments based on extensive data
available for related compounds [9,15,16] are given in Table 2. A
strong band observed in the IR spectra of 1–6 in the region of
1660–1672 cmꢁ1 can be assigned to the
absence of
m
(C@O) group. The total
m(C@O) absorption in the IR spectra of the prepared
dyes together with the appearance of new m(C@N) absorption in
the range of 1612–1616 cmꢁ1 clearly indicated that new Schiff-
base compounds had been formed in each case. The symmetric
N@N stretching mode, in the IR spectra of 1a–6a, leads to a med-
Electronic absorption spectra and substituent effects
ium band at 1470–1472 cmꢁ1, while the
m(CAO) stretching mode
The electronic absorption spectra of 1a–6a, recorded in DMSO
at room temperature display mainly three bands, Fig. 3. The first
band located at 250–270 nm can be assigned to the moderate en-
gives an intense band within the range 1283–1288 cmꢁ1. The IR
spectra of 1 and related azo-azomethine dyes, 1a, show strong
bonds at 1344–1346 and 1534–1525 cmꢁ1 assigned to the NO2
groups [29,30].
ergy
at 348–375 nm is due to low energy
the -electrons of the azo and azomethine groups [31]. On the
p ?
p⁄ transition of the aromatic rings while the second band
p
?
p⁄ transition involving
p
1H NMR spectra
other hand, the absorption spectra of 1a and 4a display a broad
band at 450–540 nm assigned to n ? p⁄ transition of azo and azo-
methine chromophores and also intramolecular charge transfer
interaction involving the whole molecule of the dye. The intramo-
lecular CT band can be assigned to the existence of tautomeric
equilibrium originating from hydroxyl group in o-position of aro-
matic ring. Examination of the results reported in Table 2, reveals
The 1H NMR spectra of the 1–6 and 1a–6a, obtained at ambient
temperature, in d6-DMSO, display a group of signals corresponding
to the hydrogens of each molecule. The slightly broad signal at dH
11.47–11.61 ppm in the 1H NMR spectra of 1–6 is assigned to the
OH protons, as was confirmed by deuterium exchange when D2O
was added to d6-DMSO solution. The OH protons of 1a–6a exhibit
a slightly broad singlet resonance at dH 13.68–13.94 ppm. The
CH@N protons of 1a–6a exhibit a singlet resonance at dH 9.02–
9.04 ppm. Also, the 1H NMR spectra of 1a–6a show two doublet,
dH 7.40–7.96 ppm and 7.75–8.35 ppm, assigned to the para-substi-
tuted aromatic ring. The doublet pattern of dH 7.75–8.35 ppm sig-
nal is simplified after irradiation of signals at 7.40–7.96 ppm. The
that the position of low energy
p ?
p⁄ band is highly influenced
by the nature of the para-substituent, R. It acquires a red shift for
kmax in the order, NO2 > Br > Cl > F ꢂ CH2CH3 > Me. This behavior
can be interpreted on the basis of the expected high delocalization
of the electrons in the para-substituted dye with nitro group which
enhances the conjugated system [32]. Also, delocalization of the
electrons in o-hydroxy substituted azo-azomethine dyes, may be
inferred from (i) selective solvation, (ii) the ability of the solvent
to form stronger intermolecular H-bonds with a particular tauto-
meric form, Fig. 4, and (iii) the intramolecular hydrogen bonding
between C@N or N@N and OH groups [9,32].
ratio
D
d/J for para-substituted aromatic ring in 4a is equal to zero,
d, between the cou-
it means that the chemical shift difference,
D
pled protons becomes zero, the middle peaks coalesce to give a sin-
gle peak, and the end peaks vanish. This situation is encountered
with equal chemical shifts for two set of protons. The AA0XX0 sys-
tem changes into an A4 system.
Solvatochromism behavior
Thermal properties
It has been accepted that the electronic transitions of azo-azo-
methine compounds strongly depend on the nature of media
[33]. For this purpose, the electronic absorption spectra of
3 ꢃ 10ꢁ5 M solution of the prepared dyes in four organic solvents
with different polarity were measured at room temperature.
The polarity and hydrogen bonding properties of the solvents
used in the present investigation, indicated by the Kamlet–Taft
In order to give more insight into the structure of the prepared
dyes, the thermal studies of the prepared dyes have been carried
out using thermogravimetry techniques. In the present investiga-
tion, the heating rates were suitably controlled at 10 °C minꢁ1 un-
der N2 atmosphere and the weight loss was measured from 25 °C
up to 900 °C.
The initial decomposition and inflection temperatures have
been used as an indication on the thermal stability of the prepared
dyes. Above 290 °C, the TG curves of the prepared compounds
parameters (
scale of solvent hydrogen-bond acceptor (HBA) basicity which re-
fers to the acceptance of the proton of a hydrogen bond. is a scale
a
, b, and p⁄) [33], are summarized in Table 4. b is a
a
Table 2
Tentative assignments of some selected IRa frequencies (cmꢁ1) and UV–Vis data of the prepared azo-azomethine dyes and their azo precursors.
Compounds
m
(CAO)
m(C@O)
m
(C@C)
m
(C@N)
m
(NO2)
m
(Phenol ring)
m
(N@N)
kmax (nm) (e
(Mꢁ1 cmꢁ1)) in DMSO
1
2
3
4
5
6
1a
2a
3a
4a
5a
6a
1288
1277
1286
1286
1286
1287
1288
1283
1285
1285
1285
1283
1666
1653
1668
1668
1672
1668
–
–
–
–
–
1608
1602
1622
1620
1620
1620
1616
1612
1616
1614
1614
1612
–
–
–
–
–
–
1616
1612
1616
1614
1614
1612
1525, 1346
–
–
–
–
–
1575
1581
1572
1572
1595
1576
1580
1580
1578
1574
1593
1580
1479
1479
1477
1475
1479
1481
1472
1470
1470
1472
1472
1470
246 (4500), 382(12700), 551 (1850)
260 (7360), 347 (16314), 447(3120)
256 (6490), 410 (7850), 466(9345)
260 (9320), 349 (18700), 456 (7049)
260 (14650), 341 (25253), 461 (5022)
260 (7580), 344 (23400), 437 (3720)
256 (36494), 374 (59973), 533 (18890)
269 (40623), 352 (62564)
1524, 1344
–
–
–
–
–
268 (30738), 354 (49604)
256 (36945), 359 (38602), 450 (12313)
261 (40352), 349 (55898)
–
257 (37500), 348(66370)
a
KBr discs.

656
H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
Table 3
Thermal analyses data for 1a–6a.
a
Compounds
Td (°C)
Temp. of steps (°C)
Mass loss (% found)
Probable (% calcd.)
Nature of fragment lost
12H9N6O5
C2H5N2OS2
C6H4
1a
311
275–360
360–600
600–900
36.45
25.04
17.71
36.93
25.18
18.18
C
2a
307
280–400
400–590
590–800
56.00
35.33
11.38
56.30
36.82
11.11
C29H28N4O2
C3H6N2S2
C2H2
3a
4a
5a
6a
308
298
297
299
260–440
440–800
62.07
30.14
61.79
28.58
C26H18Cl2N6O2
C2H4S2
240–380
380–800
54.56
35.30
54.40
36.24
C19H14Br2N5O2
C7H6S2
220–430
430–800
60.54
29.96
60.15
28.58
C26H18F2N6O2
C2H4S2
254–483
483–800
59.73
29.02
59.17
28.53
C28H24N6O2
C2H4S2
a
Thermal decomposition temperature.
Fig. 2. TG-TGA curve of 6a.
of solvent hydrogen bond donor (HBD) acidity which refer to the
donation of the proton. p⁄ is a scale of solvent dipolarity/polariz-
ability which refer to the ability of solvent to stabilize a charge
or a dipole by virtue of its dielectric effect. The p⁄ value is corre-
lated with the solvatochromic behavior values. The solvatochromic
behavior of a dye is the shift of the
p ?
p⁄ band wavelength due to
the presence of solvent with different polarity which is due to the
interaction between the solute and solvent molecules [33]. We
found that the low energy
p ?
p⁄ band generally shows batho-
chromic shift (positive solvatochromism) as the polarity of solvent
was increased. The influence of solvents for the prepared dyes in-
creases in the order DMSO > DMF > CHCl3 ꢂ THF. This positive sol-
vatochromism exhibited by the dyes may be due to the effect of
dipole moment changes of the excited state and/or changes in
Fig. 3. Electronic absorption spectra of 1a–6a in DMSO.

H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
657
N
S
S
N
Azo-imino phenol
H
H
R
N
N
OH
HO
N
N
R
N
S
S
N
Imino hydrazone
H
O
H
O
H
N
H
N
R
N
N
R
HN
S
S
NH
Azo-enaminone
H
O
H
O
R
N
N
N
N
R
Fig. 4. Structures of azo-imino phenol, imino hydrazone and azo-enaminone tautomers.
DMF solvents and this band vanishes completely in CHCl3 and
THF. This fact can be explained in according to b parameter which
is high for DMSO and DMF, Table 4. As the b parameter increases,
the ability of the solvent for accepting the proton of OH-group is
increased, too. In consequence, the formation of imino-hydrazone
and azo-enaminone tautomers is expected in DMSO and DMF solu-
tions. The absorption spectra of 4a in various solvents are shown in
Fig. 5 (for other dyes see supporting information).
Table 4
Selected physical and solvatochromic parameters (
a
, b, and p⁄), for used solvents.
Solvent
a
b
p⁄
e
l/D
THF
DMSO
DMF
0.00
0.00
0.00
0.20
0.55
0.76
0.69
0.10
0.55
1.00
0.88
0.69
7.58
1.74
4.05
3.81
1.15
46.45
36.71
4.89
CHCl3
Conclusion
In the present work six new bis-iminated water insoluble azo-
azomethine dyes were synthesized via condensation reaction of
a,
a0-bis(o-aminophenylthio)-1,2-xylene with 5-(4-substituted-
phenyl)-azo-salicyladehyde. The solvatochromic studies of the pre-
pared dyes in DMSO, DMF, CH3CN and THF was indicated that the
low energy
p ?
p⁄ band of the dyes shows bathochromic shift as
the polarity of solvent was increased.
The prepared dyes are stable up to 290 °C. According to the
thermal stability and absorption spectra, we can conclude that
these compounds may be suitable for use as recording dyes. Fur-
thermore, the presence of various coordination sites in the pre-
pared compounds makes them very versatile species, which
could potentially act as multidentate ligands.
Fig. 5. Electronic spectra of 4a in various solvents with different polarities.
Acknowledgement
the hydrogen bonding strength in polar solvents [34]. In addition, it
We are grateful to the Arak University for financial support of
this work.
should be noted that the n ? p⁄ band appears only in DMSO and

658
H. Khanmohammadi, K. Rezaeian / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 652–658
[18] Y. Zhang, Z.H. Lu, Mater. Chem. Phys. 63 (2000) 188–195.
[19] H. Jouhis, F.S. Kamounah, C. Gooijer, G. van der Zwan, L. Antonov, J. Photochem.
Photobiol. A 152 (2002) 183–191.
[20] Y. Qian, G. Wang, G. Xiao, B. Lin, Y. Cui, Dyes Pigments 75 (2005) 460–465.
[21] D.R.C. Matazo, R.A. Ando, A.C. Borin, P.S. Santos, J. Phys. Chem. A 112 (2008)
4437–4443.
[22] P.I. Nagy, W.M.F. Fabian, J. Phys. Chem. B 110 (2006) 25026–25032.
[23] H.Y. Lee, X. Song, H. Park, M.-H. Baik, D. Lee, J. Am. Chem. Soc. 132 (2010)
12133–12144.
[24] W.M.F. Fabian, L. Antonov, D. Nedeltcheva, F.S. Kamounah, P.J. Taylor, J. Phys.
Chem. A 108 (2004) 7603–7612.
[25] M.R. Yazdanbakhsh, M. Giahi, A. Mohammadi, J. Mol. Stru. 144 (2009) 145–
148.
[26] H. Khanmohammadi, M. Darvishpour, Dyes Pigments 81 (2009) 167–173.
[27] O. Ummühan, H. Alp, P. Gökçe, M. Ocak, Separ. Sci. Technol. 41 (2006) 391–
401.
[28] J. Tredwell, C.M. Keary, Chem. Phys. 43 (1979) 307–316.
[29] H. Khanmohammadi, M.H. Abnosi, A. Hosseinzadeh, M. Erfantalab,
Specterochim. Acta Part A 71 (2008) 1474–1480.
[30] G. Socrates, Infrared and Raman Characteristic Group Frequencies, third ed.,
John Wiley & Sons Ltd., 2001.
References
[1] M. Manuela, M. Raposoa, Ana M.R.C. Sousaa, A. Maurício, C. Fonsecaa, G. Kirsch,
Tetrahedron 61 (2005) 8249–8256.
[2] P.J. Coelho, L.M. Carvalho, A.M.C. Fonseca, M.M.M. Raposo, Tetrahedron Lett. 47
(2006) 3711–3714.
[3] M.A. Salvador, L.V. Reis, P. Almeida, P.F. Santos, Tetrahedron 64 (2008) 299–
303.
[4] X.Y. Li, Y.Q. Wu, D.D. Gua, F.X. Gan, Mater. Sci. Eng. B 158 (2009) 53–57.
[5] E. Rivera, M.P. Carreón-Castro, L. Rodríguez, G. Cedillo, S. Fomine, O.G. Morales-
Saavedra, Dyes Pigments 74 (2007) 396–403.
[6] F.X. Huang, Y.Q. Wu, D.H. Gu, F.X. Gan, Dyes Pigments 66 (2005) 77–82.
[7] Y. Geng, D.G. Gu, F.X. Gan, Mater. Sci. Eng. B 110 (2004) 115–118.
[8] W. Chen, Y.Q. Wu, D.H. Gu, F.X. Gan, Mater. Lett. 61 (2007) 4181–4184.
_
[9] E. Ispir, Dyes Pigments 82 (2009) 13–19.
[10] S. Alghool, H.F.A. El-Halim, A. Dahshan, J. Mol. Struct. 983 (2010) 32–38.
[11] E. Chinoporos, E.M. Idelson, P.F. King, US Patent 4656,117.
[12] Y.S. Zhou, L.J. Zhang, X.R. Zeng, J.J. Vital, X.Z. You, J. Mol. Struct. 553 (2000) 25–
30.
[13] A.K. Ghosh, K.K. Kamar, P. Paul, S.M. Peng, G.H. Lee, S. Goswami, Inorg. Chem.
41 (2002) 6343–6350.
[14] M. Odabasßog˘lu, Ç. Albayrak, R. Özkanca, F.Z. Aykan, P. Lonecke, J. Mol. Struct.
840 (2007) 71–89.
[15] M.S. Refat, I.M. El-Deen, H.K. Ibrahim, S. El-Ghool, Spectrochim. Acta Part A 65
(2006) 1208–1220.
[31] A.M. Khedr, M. Gaber, R.M. Issa, H. Erten, Dyes Pigments 67 (2005) 117–
126.
[32] A. Ghanadzadeh Gilani, M.R. Yazdanbakhsh, N. Mahmoodi, M. Moghadam, E.
Moradi, J. Mol. Liq. 139 (2008) 72–79.
[33] C. Reichardt, T. Welton, Solvents and Solvent Effects in Organic Chemistry,
fourth ed., VCH, 2011.
[34] Z. Seferog˘lu, N. Ertan, T. Hökelek, E. Sßahin, Dyes Pigments 77 (2008) 614–625.
_
[16] H. Dinçaple, F. Toker, I. Durucasu, N. Avcibasßi, S. Icli, Dyes Pigments 75 (2007)
11–24.
[17] H.K. Lee, K. Doi, H. Harada, O. Tsutsumi, A. Kanazawa, T. Shiono, T. Ikeda, J.
Phys. Chem. B 104 (2000) 7023–7028.