Synthesis and evaluation of changes induced by solvent and substituent in electronic absorption spectra of some azo disperse dyes

Article abstract of DOI:10.1016/j.saa.2011.12.062

Five azo disperse dyes were prepared by diazotizing 4′- aminoacetophenone and p-anisidine and coupling with varies N-alkylated aromatic amines. Characterization of the dyes was carried out by using UV-vis, FTIR and ¹H NMR spectroscopic techniqu

Full text of DOI:10.1016/j.saa.2011.12.062

Spectrochimica Acta Part A 89 (2012) 238–242
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and evaluation of changes induced by solvent and substituent in
electronic absorption spectra of some azo disperse dyes
Asadollah Mohammadi∗, Mohammad Reza Yazdanbakhsh, Lahya Farahnak
Department of Chemistry, Faculty of Sciences, University of Guilan, Rasht, Iran
a r t i c l e i n f o
a b s t r a c t
Five azo disperse dyes were prepared by diazotizing 4ꢀ-aminoacetophenone and p-anisidine and coupling
with varies N-alkylated aromatic amines. Characterization of the dyes was carried out by using UV–vis,
FTIR and 1H NMR spectroscopic techniques. The electronic absorption spectra of dyes are determined at
room temperature in fifteen solvents with different polarities. The solvent dependent maximum absorp-
tion band shifts, were investigated using dielectric constant (ε), refractive index (n) and Kamlet–Taft
polarity parameters (hydrogen bond donating ability (˛), hydrogen bond accepting ability (ˇ) and dipolar-
ity/polarizability polarity scale (ꢀ*)). Acceptable agreement was found between the maximum absorption
band of dyes and solvent polarity parameters especially with ꢀ*. The effect of substituents of coupler
and/or diazo component on the color of dyes was investigated. The effects of acid and base on the visible
absorption maxima of the dyes are also reported.
Article history:
Received 3 November 2011
Received in revised form
18 December 2011
Accepted 21 December 2011
Keywords:
Disperse azo dyes
Absorption spectrum
Solvent effect
Solvent parameters
Substituent effect
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
the polarity of the solvent. Moreover, absorption bands position
depends on different types of interactions between solvent and
Having versatile applications in miscellaneous areas such as
electrophotography, laser printing, reversible optical storage, non-
linear optical (NLO) devices and liquid crystalline displays (LCDs)
as well as biological–medicinal studies, azo compounds have been
of utmost importance as colorants [1–8]. The versatile usage of azo
compounds especially azobenzene dyes can be attributed to the
possession of several advantages such as intensive color, ease to
prepare from cheap, readily available starting materials, desirable
fastness properties and unique properties arising from reversible
conformational changes accompanying light induced cis–trans iso-
merization [9–11].
solute. According to complexity of the interactions between solute
and solvent, the experimental and theoretical investigations of the
structure of liquids are one of the most difficult tasks for both
physics and chemistry [16–21].
In the present work, we have synthesized four disperse
dyes with donor–acceptor substituents and one dye including
donor–donor moieties in their conjugated systems. The solva-
tochromic behavior of synthesized dyes were investigated in
solutions using the empirical solvent polarity parameters, includ-
ing solvent dipolarity/polarizability (ꢀ*), hydrogen bond donation
ability (˛) as solvent acidity, and hydrogen bond acceptance abil-
ity (ˇ) as solvent basicity, and dielectric constant (ε) and refractive
index (n) [22–24]. Also, the effects of substituent and pH on their
absorption properties of dyes were evaluated. The chemical struc-
tures of the synthesized disperse dyes are presented in Scheme 1.
Disperse dyes are one of the most important colorants that are
poorly soluble in water and are suitable for many applications from
traditional dyeing to high and modern technologies, which azo dyes
constitute the largest group of disperse dyes [12–15].
Solvatochromism studies are other fields that numerous papers
in relation with these disperse dyes have been published. It has long
been known that UV–vis/IR absorption spectra of azo dyes influ-
enced by the surrounding medium and solvents can bring about a
change in the position, intensity, and shape of absorption bands.
However the absorption properties of these dyes are affected by
solvents and showed bathochromism (positive solvatochromism)
or hypsochromism (negative solvatochromism) upon increasing
2. Experimental
2.1. Materials and apparatus
The chemicals used in this study were obtained from Merck and
Aldrich Chemical Companies and were used without further purifi-
cation. All melting points were determined on an electrothermal
melting point apparatus and are uncorrected. Elemental analyses
were performed using a Heracus CHN-O-Rapid analyzer. Infrared
spectra were recorded on a Shimadzu 8400 FT-IR spectrophotome-
ter. The proton nuclear magnetic resonance (1H NMR) spectra were
∗
Corresponding author. Tel.: +98 131 7723677; fax: +98 131 7720733.
E-mail address: a mohammadi@guilan.ac.ir (A. Mohammadi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.12.062

A. Mohammadi et al. / Spectrochimica Acta Part A 89 (2012) 238–242
239
HO
OH
OH HO
OH
CH3 CH3
N
CH3
H
N
N
N
N
N
N
N
N
N
N
N
O
N
C
N
C
N
C
C
CH3
O
CH3
O
CH3
O
CH3
O
CH3
Dye 1
Dye 2
Dye 3
Dye 4
Dye 5
Scheme 1. The chemical structure of synthesized azo dyes.
obtained on a FT-NMR (500 MHz) Brucker apparatus spectrome-
ter, and the chemical shifts are expressed in ı ppm using TMS as
an internal standard. The visible spectra were measured using a
Pharmacia Biotech Spectrophotometer.
2.2.3. 1-(4-(4-(Diethylamino)phenylazo)phenyl)ethanone (dye 3)
Red dye with metallic luster was recrystallized from DMF/H2O
and obtained in a yield of 85%.
Mp: 159–161 ◦C. UV–vis (EtOH), ꢁmax (nm) 461. IR (KBr): ꢂ
2880–2980 (Aro. H), 1502(N N). 1H NMR (CDCl3) 1.26 (t, 6H, CH3,
2.2. Synthesis and characterization
J = 7.1 Hz), 2.5 (s, 3H, CH3), 3.48 (q, 4H,
N CH2, J = 7.11 Hz), 6.72
(d, 2H, Aro. H, J = 9.26 Hz), 7.9 (d, 2H, Aro. H, J = 9.26 Hz), 7.96–8.0
(m, 4H, Aro. H). Elemental analysis calcd for C18H21N3O: C 73.08%,
H 7.09%, N 14.41%. Found: C 73.19%, H 7.17%, N 14.23%.
The mixtures of aniline derivatives (3 mmol), water (5 mL) and
concentrated sulfuric acid (7.5–9 mmol) were heated with stirring
until a clear solution was obtained. These solutions were cooled to
0–4 ◦C and a solution of sodium nitrite (0.207 g, 3 mmol) in water
was added drop wise while the temperature was maintained below
4 ◦C. The resulting mixtures were stirred for 45–60 min in an ice
bath. After diazotization was complete, the azo liquor was slowly
added to a stirred solution of aromatic amines (3 mmol) dissolved
in 10 mL of buffer solution of acetic acid–acetate sodium (pH = 5)
and 2–5 mL ethanol. The resulting mixture was stirred at 0–4 ◦C for
2 h in an ice bath. After this stage, the pH of the reaction mixture
was maintained at 6.5–7.5 by addition of acetate sodium solution.
Then the resulting dyes were filtered and washed with cold water.
The crude dyes were purified using recrystallization method with
EtOH and DMF/H2O. The physical and spectral data of the purified
dyes are as follows.
2.2.4. 1-(4-(4-(N-benzyl-N-ethylamino)phenylazo)phenyl)
ethanone (dye 4)
Red dye with metallic luster was recrystallized from DMF/H2O
and obtained in a yield of 85%.
Mp: 116–118 ◦C. UV–vis (EtOH), ꢁmax (nm) 447. IR (KBr): ꢂ
2875–2990 (Aro. H), 1510 (N N). 1H NMR (CDCl3) 1.3 (t, 3H, CH3,
J = 7.12 Hz), 3.6 (q, 2H,
N CH2, J = 7.12 Hz), 4.2 (s, 2H, CH2), 6.7
(d, 2H, J = 9.1 Hz, Aro. H), 7.2 (d, 2H, J = 9.1 Hz, Aro. H), 7.3 (d, 2H,
J = 8.8 Hz, Aro. H), 7.7 (d, 2H, J = 8.8 Hz, Aro. H). Elemental analysis
calcd for C23H23N3O: C 77.32%, H 6.75%, N 11.82%. Found: C 77.28%,
H 6.49%, N 11.76%.
2.2.5. 2,2ꢀ-(4-(4-Methoxyphenylazo)phenylamino)diethanol (dye
5)
Golden dye with metallic luster was recrystallized from EtOH
and obtained in a yield of 94%.
2.2.1. 2-(4-(4-Acetylphenylazo)phenylamino)ethanol (dye 1)
Orange dye was recrystallized from EtOH and obtained in a yield
of 90%.
Mp: 135–137 ◦C. UV–vis (EtOH), ꢁmax (nm) 409. IR (KBr): ꢂ 3445
(OH), 2960 (Aro. H), 1504 (N N) cm−1 1H NMR (CDCl3) ı 3.23 (br,
.
Mp: 126–128 ◦C. UV–vis (EtOH), ꢁmax (nm) 368. IR (KBr): ꢂ
3310–3450 (br, OH and NH, overlapped), 1495 (N N) cm−1 1H
.
2H, OH), 3.72 (t, 4H, N–CH2, J = 4.74 Hz), 3.91 (s, 3H, CH3), 3.96 (t,
4H, O–CH2, J = 4.88 Hz), 6.79 (m, 2H, Aro. H), 7.03 (m, 2H, Aro. H),
7.87 (m, 4H, Aro. H). Elemental analysis calcd for C17H21N3O3: C
64.32%, H 7.1%, N 13.63%. Found: C 64.74%, H 6.71%, N 13.32%.
NMR (DMSO-d6) ı 2.4 (1H, t, J = 5.3 Hz, OH), 2.47 (3H, s, CH3), 3.8
(2H, q, J = 5.4 Hz, OCH2), 4.3 (2H, t, J = 5.3 Hz, NCH2), 4.6 (1H, br, s,
NH), 6.9 (2H, d, J = 8.8 Hz, Aro. H), 7.94 (2H, d, J = 8.9 Hz, Aro. H),
7.96 (2H, d, J = 8.9 Hz, Aro. H), 8.1 (2H, d, J = 8.9 Hz, Aro. H). Ele-
mental analysis calcd for C16H17N3O2: C 67.64%, H 6.22%, N 15.23%.
Found: C 67.83%, H 6.05%, N 14.83%.
3. Results and discussion
3.1. The UV–visible spectra and solvatochromic studies of
synthesized dyes
2.2.2. 2,2ꢀ-(4-(4-Acetylphenylazo)phenylamino)diethanol (dye 2)
Orange-red dye with metallic luster was recrystallized from
EtOH and obtained in a yield of 94%.
In order to study of solvent effects on spectral features of the
dyes, we recorded their absorption spectra in various solvents with
different polarity at a concentration of 10−5–10−6 M in the range
of 300–700 nm (Table 1), in which the solvents are arranged in
the order of increasing polarity. Also, refractive index (n), dielec-
tric constant (ε) and the solvatochromic parameters (ꢀ*, ˛, and ˇ)
were taken from the literature [22–24]. As shown in Table 1, the
electronic absorption spectra of all studied compounds in different
Mp: 156–158 ◦C. UV–vis (EtOH), ꢁmax (nm) 449. IR (KBr): ꢂ 3280
(br, OH), 1660 (
C .
O), 1510 (N N) cm−1 1H NMR (DMSO-d6) ı
2.51 (s, 3H, CH3), 3.56 (t, 4H, N–CH2, J = 4.99 Hz), 3.73 (q, 4H, O CH2,
J = 5.19 Hz), 4.59 (t, 2H, OH, J = 5.34 Hz), 6.70 (m, 2H, Aro. H), 7.74
(m, 4H, Aro. H), 7.92 (m, 2H, Aro. H). Elemental analysis calcd for
C18H21N3O3: C 65.82%, H 6.75%, N 14.8%. Found: C 66.04%, H 6.47%,
N 12.84%.

240
A. Mohammadi et al. / Spectrochimica Acta Part A 89 (2012) 238–242
Table 1
Experimental electronic absorption maxima for investigated dyes and solvent parameters [22–24].
Solvents
ꢀ*
˛
ˇ
ε
n
ꢁmax (nm)
293 K
293 K
Dye 1
Dye 2
Dye 3
Dye 4
Dye 5
n-Hexane
−0.081
0.00
0.27
0.28
0.54
0.54
0.55
0.58
0.58
0.60
0.71
0.75
0.82
0.87
1.00
0.00
0.00
0.00
0.00
0.00
0.83
0.00
0.44
0.00
0.93
0.08
0.19
0.30
0.00
0.00
0.00
0.00
0.47
0.00
0.45
0.77
0.37
0.00
0.55
0.62
0.48
0.31
0.00
0.69
0.76
1.89
2.02
4.27
2.24
6.08
25.33
2.22
4.81
1.3748
1.4226
1.3526
1.4601
1.3723
1.3611
1.4224
1.4459
1.4070
1.3288
1.3588
1.3442
1.4242
1.4305
1.4770
359
362
364
356
366
368
366
359
361
365
367
368
365
403
412
424
430
437
431
444
449
443
434
448
441
448
449
435
466
473
430
433
449
455
457
461
447
457
459
457
458
458
459
477
485
426
429
440
443
445
445
442
443
445
439
445
446
448
460
465
392
398
407
401
411
409
412
404
413
407
413
413
407
422
425
Cyclohexane
Diethyl ether
Tetrachloromethane
Ethyl acetate
Ethanol
Dioxane
Chloroform
Tetrahydrofuran
Methanol
7.47
33.10
21.01
37.50
9.08
38.25
47.24
Acetone
Acetonitrile
Dichloromethane
DMF
DMSO
Table 2
solvents exhibit maximum absorption band (ꢁmax) in the range of
361–485 nm which can be attributed to n → ꢀ* and/or ꢀ–ꢀ* elec-
tronic transitions of azo chromophores [25]. The dyes displayed a
single main absorption peak without a shoulder in all solvents. The
ꢁmax of all compounds were found to show a strong solvent depen-
dency, denoting bathochromic effect (positive solvatochromism)
in more polar solvents, except for chlorinated solvents. For chlo-
rinated solvents the deviation may be due to unique interactions
between the polychlorinated solvents and the solute molecules.
Such interactions can be accounted using another specific sol-
vent polarity scale named as delta (ı) that generally is used in
multi-parameter correlation. The spectral shift is mainly due to
solute–solvent interactions that give rise to a better stabilization of
the ꢀ* orbital as compared to the ꢀ orbital in polar solvents (Fig. 1).
It is well known that the position and shape of absorption spec-
tra changes with solvent nature. The changes induced by solvents
were evaluated using solvatochromic parameters such as (n and ε)
and (ꢀ*, ˛ and ˇ). In order to the more studies of solvatochromic
properties of synthesized dyes, we were obtained the correlation
coefficient values between maximum wavelength (ꢁmax) of dyes
and solvent parameters (Table 2). The investigations of data in
Table 2 indicate that there was regular change between the ꢁmax
values of the compounds and ꢀ*, ε and ˇ values of studied solvents.
On the other hand, all studied dyes, exhibit a bathochromic shift
(red shift) as a result of an increase in the solvent polarity scale (ꢀ*),
hydrogen bond accepting ability (ˇ). Therefore, it can be concluded
that the most important contributions to the solvatochromism
shift arise from ꢀ* and ˇ terms of solvent parameters. This effect
was attributed to the interaction of solvents such as DMF and
DMSO with non-bonding electron pair on nitrogen atom in coupler
Correlation coefficient (R) of dyes in studied solvents.
Solvent parameters
Dye no.
ꢀ*
˛
ˇ
ε
n
R
a
R
R1
R
R
R
Dye 1
Dye 2
Dye 3
Dye 4
Dye 5
0.40
0.63
0.80
0.80
0.77
0.47
0.85
0.87
0.85
0.91
0.027
0.002
0.011
0.004
0.008
0.37
0.66
0.42
0.35
0.58
0.58
0.67
0.56
0.47
0.51
0.13
0.03
0.09
0.16
0.03
a
Correlation coefficient (R1) obtained without chlorinated solvents.
component of synthesized dyes, which increases the electron den-
sity at the nitrogen atom. Also, no linear correlation was obtained
when solvent parameters n and ˛ were applied. Thus, the correla-
tion coefficient values obtained for synthesized disperse dyes show
that a major contribution to the solvatochromism is due to the
solvent dipolarity/polarizability (Fig. 2), hydrogen bond accepting
ability (Fig. 3) and dielectric constant (Fig. 4).
In the next part of the investigation, the pH values of the
synthesized dyes were also determined spectrophotometrically in
80% (v/v) ethanol–water mixtures (aqueous hydrochloric acid and
sodium hydroxide) at 25 2 ◦C. A digital pH meter Genway model
3505 was employed for determination of pH. The instrument was
accurate to 0.01 pH unit (Table 3). It was calibrated using two
standard Genway buffer solutions at pH = 4.01 and 7.00 and used
relation of Van Uitert and Haas [26]. Comparison of absorption max-
ima of the dyes revealed a red shift in ꢁmax of the main visible band
in acidic solutions. This shift can be explained on the basis that the
dyes especially dye 5 with donor–donor substituent groups exist in
2.00
1.80
1.60
500
Dye 4
y = 28.51x + 428.8
R² = 0.800
480
460
440
420
400
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
n-Hexane
Diethyl ether
Ethanol
Dioxane
Methanol
Acetonitrile
DMSO
300
400
500
600
0.00
0.20
0.40
0.60
0.80
1.00
1.20
λ (nm)
π *
Fig. 1. Electronic absorption spectra of dye 4 in different solvents.
Fig. 2. Variation of ꢁmax (nm) of dye 4 as a function of ꢀ*.

A. Mohammadi et al. / Spectrochimica Acta Part A 89 (2012) 238–242
241
Table 3
Electronic absorption spectral data of compounds 1–5 in acidic and basic solution.
Dye no.
ꢁmax (nm)
pH = 1
pH = 3
pH = 5
pH = 6
pH = 7
pH = 8
pH = 9
pH = 11
pH = 13
1
2
3
4
5
454
504
511
521
553
411
492
503
518
386
475
488
471
372
466
472
451
369
448
461
446
400
369
449
460
446
409
372
449
462
447
410
373
451
463
447
410
377
454
468
449
416
408, 560
408, 555
408, 562
N
N(CH2CH2OH)2
N
N
N(CH2CH2OH)2
H
H3CO
N
H3CO
H
Scheme 2. Acid–base equilibrium of dye 5.
500
2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Dye 4
y = 19.40x + 436.9
R² = 0.350
pH=1
480
460
440
420
400
pH=3
pH=5
pH=6
pH=7
pH=8
pH=9
pH=13
325 375 425 475 525 575 625 675 725
0.00
0.20
0.40
0.60
0.80
1.00
λ (nm)
β
Fig. 5. Absorption spectra of dye 5 in acidic and basic solutions.
Fig. 3. Variation of ꢁmax (nm) of dye 4 as a function of ˇ.
of synthesized dyes 1–4 are increased by introducing an
electron-accepting acyl group into the para-position of benzenoid
system, caused bathochromic shifts relative to similar dye 5 includ-
ing an electron-donating methoxy group. Therefore dyes 1–4
showed bathochromic shift due to extended resonance system
in comparison with dye 5 in all studied solvents as shown in
Table 1. In addition, the introduction of electron donating alkyl
groups in the coupler components are affected in absorption band
shifts and resulted in bathochromic shifts in all solvents (e.g. for
dye 1, ꢁmax = 368 nm relative to dye 2, ꢁmax = 449 nm or dye 3,
ꢁmax = 461 nm in ethanol).
acid–base equilibrium (Scheme 2). Considering the ꢁmax in Table 3,
these dyes in acidic solutions shifts to higher wavelengths, which
are probably related to the prominence of hydrazone forms in acidic
medium, while in neutral and basic solutions the dyes exists in
azo forms. The UV–vis spectroscopic study on dye 5 clearly indi-
cates that the present dye exists in acid–base equilibrium forms in
solution with pH = 3, 5 and 6 as shown in Fig. 5.
It was also observed that the absorption curves of the dyes were
not significantly sensitive to base solutions.
3.2. Substituent effects
4. Conclusions
In our previous work, we have demonstrated that absorp-
tion maxima of azobenzene dyes are strongly influenced with
substituents in para-position in contrast to ortho- and meta-
positions [27]. As expected, the donor–acceptor polarization
In summary, we have synthesized five disperse azo dyes 1–5
in this paper. The structures of prepared dyes were confirmed
by 1H NMR, FTIR and UV–vis spectra. The electronic absorption
spectra of disperse dyes were recorded in solvents with different
physical–chemical properties. A large bathochromic shift (positive
solvatochromism) of these compounds was observed upon increas-
ing the solvent polarity. The influence of the pH changes on the dyes
considered by comparison of the absorption maxima of these dyes
in solutions with different pH, this fact directed us to the conclu-
sion that the dye 5 having donor–donor substituent groups exist in
acid–base equilibrium forms. Also, introduction of acyl group in the
diazo component ring or alkyl amino group in the coupling compo-
nent ring resulted in the bathochromic effect in studied solvents.
500
Dye 4
y = 0.417x + 437.3
R² = 0.475
480
460
440
420
400
Acknowledgment
0
10
20
30
40
50
ε
The authors are very grateful to the Guilan University for pro-
viding financial support of this study.
Fig. 4. Variation of ꢁmax (nm) of dye 4 as a function of ε.

242
A. Mohammadi et al. / Spectrochimica Acta Part A 89 (2012) 238–242
References
[13] J.J. Lee, W.J. Lee, J.H. Choi, J.P. Kim, Synthesis and application of temporarily
solubilised azo disperse dyes containing b-sulphatoethylsulphonyl group, Dyes
Pigments 65 (2005) 75–81.
[1] T. Xie, D. Wang, L. Zhu, C. Wang, T. Li, X. Zhou, M. Wang, Application of sur-
face photovoltage technique to the determination of conduction types of azo
pigment films, J. Phys. Chem. B 104 (2000) 8177–8181.
[2] L. Lucarelli, V. Nadtochenko, J. Kiwi, Environmental photochemistry: quantita-
tive adsorption and FTIR studies during the TiO2-photocatalyzed degradation
of orange II, Langmuir 16 (2000) 1102–1108.
[3] Y. Qian, G. Wang, G. Xiao, B. Lin, Y. Cui, The first-order molecular hyperpolariz-
ability and thermal stability of charge-transfer azo diol and azo aldimine, Dyes
Pigments 75 (2007) 460–465.
[4] F. Qiu, Y. Cao, H. Xu, Y. Jiang, Y. Zhou, J. Liu, Synthesis and properties of poly-
mer containing azo-dye chromophores for nonlinear optical applications, Dyes
Pigments 75 (2007) 454–459.
[5] B.K. So, H.J. Kim, S.M. Lee, H.H. Song, J.H. Park, Novel bent-shaped liquid
crystalline compounds. IV. Dimesogenic compounds containing 2-hydroxy-
1,3-dioxypropylene and azobenzene mesogens, Dyes Pigments 70 (2006)
38–42.
[6] R. Gimenez, M. Millaruelo, M. Pinol, J.L. Serrano, A. Vinuales, R. Rosenhauer, T.
Fischer, J. Stumpe, Synthesis thermal and optical properties of liquid crystalline
terpolymers containing azobenzene and dye moieties, Polymer 46 (2005)
9230–9242.
[7] K. Krohn, M. John, E.I. Demikhov, New aromatic azo compounds: syntheses and
liquid-crystalline properties, Russ. Chem. Bull. Int. Ed. 50 (2001) 1248–1254.
[8] A.O. Alnajjar, M.E. El-Zaria, Synthesis and characterization of novel azo-
morphine derivatives for possible use in abused drugs analysis, Eur. J. Med.
Chem. 43 (2008) 357–363.
[9] Y. Yua, T. Ikeda, Alignment modulation of azobenzene-containing liquid crystal
systems by photochemical reactions, J. Photochem. Photobiol. C: Photochem.
Rev. 5 (2004) 247–265.
[14] M.R. Yazdanbakhsh, A. Mohammadi, M. Abbasnia, Some heterocyclic azo dyes
derived from thiazolyl derivatives; synthesis; substituent effects and solva-
tochromic studies, Spectrochim. Acta A 77 (2010) 1084–1087.
[15] H.R. Maradiya, Disperse dyes derived from 2-amino-5-mercapto-1,3,4-
thiadiazole, Chem. Heterocycl. Compd. 45 (2009) 1558–1563.
[16] M.M.M. Raposo, A.M.R.C. Sousa, A.M.C. Fonseca, G. Kirsch, Thienylpyrrole azo
dyes: synthesis, solvatochromic and electrochemical properties, Tetrahedron
61 (2005) 8249–8256.
[17] Y.H. Ebeada, M.A. Selim, S.A. Ibrahim, Solvatochromic, acid–base features and
time effect of some azo dyes derived from 1,3-benzothiazol-2-ylacetonitrile:
experimental and semiempirical investigations, Spectrochim. Acta A 75 (2010)
760–768.
[18] F. Karci, F. Karcı, The synthesis and solvatochromic properties of some novel
heterocyclic disazo dyes derived from barbituric acid, Dyes Pigments 77 (2008)
451–456.
[19] A.G. Gilani, M.R. Yazdanbakhsh, N. Mahmoodi, M. Moghadam, E. Moradi, Solva-
tochromism and dichroism of fluorinated azoquinolin-8-ol dyes in liquid and
liquid crystalline solutions, J. Mol. Liq. 139 (2008) 72–79.
[20] E. Rusu, D.O. Dorohoi, A. Airinei, Solvatochromic effects in the absorption spec-
tra of some azobenzene compounds, J. Mol. Struct. 887 (2008) 216–219.
[21] Y.G. Sıdır, I. Sıdır, H. Berber, E. Tas¸ al, UV-spectral changes for some azo com-
pounds in the presence of different solvents, J. Mol. Liq. 162 (2011) 148–154.
[22] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, 3rd ed., Wiley-
VCH, Weinheim, 2003.
[23] M.J. Kamlet, J.L. Abboud, M.H. Abraham, R.W. Taft, linear solvation energy rela-
tionship: 23: a comprehensive collection of the solvatochromatic parameters
p, a and b and some methods for simplifying the generalized solvatochromatic
equation, J. Org. Chem. 48 (1983) 2877–2887.
[24] D.R. Lide (Ed.), Handbook of Chemistry and Physics, 76th ed., CRC Press, Boca
Raton, 1995.
[25] C. Toro, A. Thibert, L. De Boni, A.E. Masunov, F.E. Hernandez, Fluorescence emis-
sion of Disperse Red 1 in solution at room temperature, J. Phys. Chem. B 112
(2008) 929–937.
[10] M.M.M. Raposo, A.M.C. Fonseca, M.C.R. Castro, M. Belsley, M.F.S. Cardoso, L.M.
Carvalho, P.J. Coelho, Synthesis and characterization of novel diazenes bear-
ing pyrrole, thiophene and thiazole heterocycles as efficient photochromic and
nonlinear optical (NLO) materials, Dyes Pigments 91 (2011) 62–73.
[11] M.R. Yazdanbakhsh, A. Mohammadi, E. Mohajerani, H. Nemati, N. Hosain Nataj,
A. Moheghi, E. Naeemikhah, Novel azo disperse dyes derived from N-benzyl–N-
ethyl–aniline: synthesis, solvatochromic and optical properties, J. Mol. Liq. 151
(2010) 107–112.
[26] L.G. Van Uitert, C.G. Haas, A method for determining thermodynamic equilib-
rium constants in mixed solvents, J. Am. Chem. Soc. 75 (1953) 451–455.
[27] M.R. Yazdanbakhsh, M. Giahi, A. Mohammadi, Synthesis and solvatochromic
properties of some new disperse azo dyes derived from 2-anilinoethanol, J.
Mol. Liq. 144 (2009) 145–148.
[12] J. Geng, T. Tao, S.J. Fu, W. You, W. Huang, Structural investigations on four het-
erocyclic Disperse Red azo dyes having the same benzothiazole/azo/benzene
skeleton, Dyes Pigments 90 (2011) 65–70.