Synthesis, solvatochromic properties and theoretical calculation of some novel disazo indole dyes

Article abstract of DOI:10.1016/j.molliq.2014.09.019

Synthesis of new disazo indole dyes (3a-3m) was carried out by diazotization of 5-amino-4-arylazo-3-methyl-1H-pyrazoles (2a-2m) and coupling with 2-phenyl indole. The newly synthesized 12 disperse disazo dyes were characterized by UV-vis, FT-IR, ¹

Full text of DOI:10.1016/j.molliq.2014.09.019

Journal of Molecular Liquids 199 (2014) 227–236
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Synthesis, solvatochromic properties and theoretical calculation of some
novel disazo indole dyes
⁎
Çiğdem Karabacak , Omer Dilek
Süleyman Demirel University, Science & Arts Faculty, Chemistry Department, 32260 Isparta, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 April 2014
Received in revised form 2 September 2014
Accepted 11 September 2014
Available online 16 September 2014
Synthesis of new disazo indole dyes (3a–3m) was carried out by diazotization of 5-amino-4-arylazo-3-methyl-
1H-pyrazoles (2a–2m) and coupling with 2-phenyl indole. The newly synthesized 12 disperse disazo dyes
were characterized by UV–vis, FT-IR, 1H NMR and elemental analysis. Their solvatochromic properties in different
solvents were investigated. In addition, theoretical calculations are performed for the disazo dyes. The molecular
structures of all synthesized dyes 3a–3m have been optimized to the global minima at the levels of using HF and
DFT methods with 6-31G(d), 6-311G(d), 6-311++G(d,p), and 6-31++G(d,p) basis sets.
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Indole
Heterocyclic dye
Diazo coupling reaction
Spectroscopic property
Theoretical calculation
1. Introduction
component. Heterocyclic compounds are used as both diazo component
and coupling component.
Azo dyes are organic compounds consisting of a diazotized amine
coupled to a coupling component and contain one or more azo
(\N_N\) linkages. In recent years, because of their properties, consid-
erable attention has been drawn toward the synthesis of azo dyes. Azo
dyes are the largest class of industrial synthesized organic dyes due to
their applications, such as dye sensitized solar cells [1], non-linear opti-
cal systems [2], metallochromic indicators [3], sensors [4], photochro-
mic materials [5], photo-sensitizers [6], biological–medical studies [7]
and computational studies [8]. Explorations of disazo dyes having aro-
matic heterocycles are very significant because they have shown bril-
liant color, excellent light, good tinctorial strength and washing
fastness. Pyrazole and indole dyes have been shown to be important col-
orants for yellow to orange dyes in industrial applications. Also, due to
their piquant electronic and geometrical features, theoretical calcula-
tions of heterocyclic compounds have been trend by several research
groups [9,10]. The biological importance of indole and its pharmacolog-
ical and medical potential have made indole extremely fascinating and
rewarding research targets and have motivated researchers to study
its synthesis and investigation on its properties [11,12].
It is very important to synthesize and characterize new disazo dyes
experimentally to provide guidance for further studies. So, in this
study, synthesis of new disazo indole dyes (3a–3m) was carried
out by diazotization of 5-amino-4-arylazo-3-methyl-1H-pyrazoles
(2a–2m) and coupling with 2-phenyl indole. All synthesized disperse
disazo dyes were characterized by UV–vis, FT-IR, 1H NMR and elemental
analysis. Their solvatochromic properties in different solvents were in-
vestigated. Also, the vibrational frequencies and optimized structure
parameters of heterocyclic disazo dye (3a–3m) have been calculated
by using HF and DFT methods at 6-31G(d,p) basis set level. All
computations have been performed using Gaussian 09.A1 package and
GaussView 5.0.8 molecular visualization program on personal comput-
er. All spectroscopic properties examined with the experimental tech-
niques were supported with the computed results.
2. Experimental
2.1. Material and methods
In the literature, one study was found on synthesis of indole disazo
dyes [13]. In that study, 4,4′-diaminodiphenylsulfonamide (DADPSA)
and 4,4′-diaminodiphenylurea (DADPU) are used as carbocyclic diazo
Chemicals used for the synthesis of the compounds were obtained
from Aldrich and Merck Chemical Company without further purifica-
tion. The solvents used were of spectroscopic grade.
IR spectra were determined using a Schimadzu IR Prestige-21
Fourier Transform-infrared (FT-IR) spectrophotometer on a KBr disc.
Nuclear magnetic resonance (1H NMR) spectra were recorded on a
Bruker Ultrashield Superconducting 400 MHz NMR in deuterated
⁎
Corresponding author.
E-mail address: cigdemkarabacak@sdu.edu.tr (Ç. Karabacak).
http://dx.doi.org/10.1016/j.molliq.2014.09.019
0167-7322/© 2014 Elsevier B.V. All rights reserved.

228
Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
NH2NH2
NC
H
NH2
CNH
NH
C C
NH2
CH3
N N C
H
N N
H3C
NH2
X
X
X
CH3
N
H
N
1a-1m
2a-2m
a, X: o-NO2
b, X: m-NO2
c, X: p-NO2
d, X: o-CH3
e, X: m-CH3
f, X: p-CH3
h, X: m-OCH3
i, X: p-OCH3
j, X: o-Cl
k, X:m-Cl
l, X: p-Cl
m: X: H
Fig. 1. Synthesis of 2-arylhydrazono-3-ketiminobutyronitriles (1a–1m) and 5-amino-4-arylazo-3-methyl-1H-pyrazoles (2a–2m).
Fig. 2. Synthesis of 2-phenyl-3-(3-methyl-4-arylazo-5-diazenyl-1H-pyrazole)-1H-indole (3a–3m).
dimethylsulfoxide (DMSO-d6) using tetramethylsilane (TMS) as the in-
ternal reference; chemical shifts were (δ) given in ppm. Ultraviolet–
visible (UV–vis) absorption spectra were recorded on a Schimadzu
UV-1601 double beam spectrophotometer at the wavelength of
maximum absorption (λmax) in a range of solvents, i.e. DMSO, DMF,
acetonitrile, methanol, acetic acid and chloroform at the various con-
centrations (1 × 10−6–1 × 10−8). Melting points were determined on
an Electrothermal 9100 melting point apparatus and are uncorrected.
Elemental analysis was done on a Leco CHNS-932 analyzer. LC-ESI-MS
analyses were recorded on Agilent 1100 MSD.
Table 1
Elemental analysis of dyes 3a–3m.
Dye
X
m.p. (°C)
Yield (%)
Color
Molecular formula (m. wt)
Elemental analysis: calc. (found)
%C
%H
%N
3a
3b
3c
3d
3e
3f
o-NO2
m-NO2
p-NO2
o-CH3
m-CH3
p-CH3
m-OCH3
p-OCH3
o-Cl
237–238
304–305
255–256
250–251
203–204
237–238
210–211
244–245
261–262
75
72
76
68
69
65
63
68
70
73
71
68
Dark red
Dark red
Dark red
Light red
Dark red
Red
C24H18N8O2
(450.45)
C24H18N8O2
(450.45)
C24H18N8O2
(450.45)
C25H21N7
(419.48)
C25H21N7
(419.48)
C25H21N7
(419.48)
C25H21N7O
(435.48)
C25H21N7O
(435.48)
63.99 (63.92)
4.03 (4.10)
24.88 (24.68)
63.99 (63.94)
63.99 (63.94)
71.58 (71.60)
71.58 (71.61)
71.58 (71.56)
68.95 (68.98)
68.95 (68.96)
65.53 (65.55)
65.53 (65.50)
65.53 (65.51)
71.09 (71.10)
4.03 (4.02)
4.03 (4.10)
5.05 (5.08)
5.05 (5.06)
5.05 (5.07)
4.86 (4.84)
4.86 (4.88)
4.12 (4.10)
4.12 (4.14)
4.12 (4.11)
4.72 (4.73)
24.88 (24.68)
24.88 (24.68)
23.37 (23.32)
23.37 (23.33)
23.37 (23.37)
22.51 (22.53)
22.51 (22.49)
22.29 (22.32)
22.29 (22.27)
22.29 (22.30)
24.18 (24.16)
3h
3i
Dark red
Red
3j
Red
C
24H18N7Cl
(439.90)
24H18N7Cl
(439.90)
24H18N7Cl
(439.90)
24H19N7
(405.45)
3k
3l
m-Cl
100–101
(decomposition)
234–235
Light red
Red
C
p-Cl
C
3m
H
197–198
Dark red
C

Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
229
Fig. 3. Tautomeric structures of 3a–3m.
2.2. Synthesis of azo dyes
of 2-arylhydrazono-3-ketiminobutyronitriles and 5-amino-4-arylazo-
3-methyl-1H-pyrazoles is shown in Fig. 1.
2.2.1. Synthesis of 2-arylhydrazono-3-ketiminobutyronitriles (1a–1m) and
5-amino-4-arylazo-3-methyl-1H-pyrazoles (2a–2m)
2-Arylhydrazono-3-ketiminobutyronitriles (1a–1m) and 5-amino-
4-arylazo-3-methyl-1H-pyrazoles (2a–2m) were prepared according
to the literature procedures [14,15]. The general route for the synthesis
2.2.2. Synthesis of 2-phenyl-3-(3-methyl-4-arylazo-5-diazenyl-1H-
pyrazole)-1H-indole (3a–3m)
5-Amino-4-arylazo-3-methyl-1H-pyrazoles (2a–2m) (0.63 g,
3.0 mmol) were dissolved in hot glacial acetic acid/propionic acid
Table 2
Spectral data for dyes 3a–3m.
FT-IR (cm−1, KBr)
νAr–H
1H NMR (d, ppm, in DMSO-d6)
νAlip–H
νN_N
Aro.–H
Alip.–H
X–H
3a
3b
3c
3d
3e
3f
3350
2958
1525
8.52–7.30 (m, 13H)
2.41 (s, 3H, pyrazole CH3)
12.59 (indole or T1) (br)
13.56 (pyrazole or T2) (br)
12.58 (indole or T1) (br)
13.53 (pyrazole or T2) (br)
12.49–12.75 (indole or T1)
13.59 (pyrazole or T2) (br)
8,40 (indole or T1) (br)
8,80 (pyrazole or T2) (br)
8.50 (indole or T1) (br)
11.50 (pyrazole or T2) (br)
8.10 (indole or T1) (br)
8.72 (pyrazole or T2) (br)
8.70 (indole or T1) (br)
8.98 (pyrazole or T2) (br)
8.40 (indole or T1) (br)
8.80 (pyrazole or T2) (br)
8.05 (indole or T1) (br)
8.85 (pyrazole or T2) (br)
8.70 (indole or T1) (br)
10.65 (pyrazole or T2) (br)
8.68 (indole or T1) (br)
9.8 (pyrazole or T2) (br)
8.20 (indole or T1) (br)
8.96 (pyrazole or T2) (br)
3172
3186
3080
3320
3240
3320
3110
3040
3320
3310
3200
2966
2920
2890
2975
2925
2820
2886
2968
2947
2892
2920
1533
1520
1550
1540
1530
1540
1540
1570
1540
1550
1535
8.66–7.33 (m, 13H)
8.65–7.19 (m, 13H)
8.96–7.21 (m, 13H)
8.68–6.92 (m, 13H)
8.90–7.11 (m, 13H)
8.25–6.95 (m, 13H)
8.10–6.89 (m, 13H)
8.18–7.08 (m, 13H)
8.20–6.97 (m, 13H)
8.22–7.18 (m, 13H)
8.6–7.10 (m, 14H)
2.56, (s, 3H, pyrazole CH3)
2.56 (s, 3H, pyrazole CH3)
1.3 (s, 3H, toluidine CH3)
2.63 (s, 3H, pyrazole CH3)
2.16–2.20 (s, 3H, toluidine CH3)
2.37–2.40 (s, 3H, pyrazole CH3)
1.18–1.19 (s, 3H, toluidine CH3)
2.40–2.60 (s, 3H, pyrazole CH3)
2.56 (s, 3H, pyrazole CH3)
3.85 (s, 3H, anisidine OCH3)
2.65–2.67 (s, 3H, pyrazole CH3)
3.94 (s, 3H, anisidine OCH3)
2.70 (s, 3H, pyrazole CH3)
3h
3i
3j
3k
3l
2.60 (s, 3H, pyrazole CH3)
2.55 (s, 3H, pyrazole CH3)
2.5 (s, 3H, pyrazole CH3)
3m
T1: hydrazo form of indole.
T2: hydrazo form of pyrazole.

230
Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
mixture (2:1, 9.0 ml) and were speedily cooled in an ice–salt bath to
−5 °C. The mixture was then stirred for 4 h at 0–5 °C. The solution
was then added in pieces during 1 h to a cold solution of nitrosyl sulfuric
acid [prepared from sodium nitrite (0.22 g) and concentrated sulfuric
acid (4.5 ml)]. The mixture was stirred 4 h at 0 °C after addition. The
progress of the reaction was followed with pH meter. Excess nitrous
acid was removed by the addition of urea. The resulting diazonium
salt was added to cold solution of 2-phenylindole (0.58 g, 3.0 mmol)
dissolved in a mixture of acetic acid/propionic acid (3:1, 12 ml). During
the addition of diazonium salt, the reaction mixture was stirred and pH
was maintained at 4–6 by addition of saturated sodium carbonate solu-
tion. The mixture was stirred for a further 24 h at 5 °C. The resulting
product was filtered, washed with water several times, dried in a
vacuum oven at 50 °C and crystallized from DMF–H2O. The general
route for the synthesis of 2-phenyl-3-(3-methyl-4-arylazo-5-diazenyl-
1H-pyrazole)-1H-indole (3a–3m) is shown in Fig. 2.
2.3. Theoretical calculations
Gaussian approximates orbital shapes and orbital energies of a given
molecular geometry using a model chemistry consisting of two parts: a
basis set and a method. Calculations using large basis sets are more ac-
curate because they are less restrictive on the location of the electrons.
Such calculations are also more expensive because they require com-
puting more integrals. DFT methods account for electron correlation
by estimating the interaction of an electron with the total electron
Fig. 4. 1H NMR spectra of dyes 3a and 3b.

Table 3
Theoretical NMR calculations for dyes 3a–3m.
6–31G(d)
6–311G(d)
Aro.–H
6–311++G(d,p)
6–31++G(d,p)
Aro.–H
Alip.–H
X–H
Alip.–H
X–H
Aro.–H
Alip.–H
X–H
Aro.–H
Alip.–H
X–H
3a
3b
3c
3d
3e
3f
8.75–7.21 2.47–2.21
7.64
(indole or T1)
9.01
(pyrazole or T2)
7.60
(indole or T1)
9.11
(pyrazole or T2)
7.67
(indole or T1)
9.11
(pyrazole or T2)
7.56
9.02–7.48 2.70–2.49
7.98 (indole or T1)
9.24 (pyrazole or T2) (m, 13H)
9.13–7.64 2.62–2.50
8.39
(indole or T1)
9.68
(pyrazole or T2)
8.46
(indole or T1)
9.84
(pyrazole or T2)
8.44
(indole or T1)
9.85
(pyrazole or T2)
8.37
9.29–7.65 2.68–2.44
8.50
(m, 13H)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3)
(s, 3H, pyrazole CH3)
(s, 3H, pyrazole CH3)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3) (indole or T1)
9.90
(pyrazole or T2)
8.68
9.05–7.24 2.47–2.23
9.35–7.51 2.71–2.69
7.93 (indole or T1)
9.34 (pyrazole or T2) (m, 13H)
9.52–7.70 2.76–2.73
9.67–7.71 2.73–2.42
(m,13H)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3) (indole or T1)
10.00
(pyrazole or T2)
8.57
8.78–7.24 2.48–2.22
9.05–7.50 2.73–2.50
8.01 (indole or T1)
9.35 (pyrazole or T2) (m, 13H)
9.29–7.62 2.78–2.54
9.27–7.66 2.76–2.43
(m,13H)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3)
(m, 13H)
(s, 3H, pyrazole CH3) (indole or T1)
10.03
(pyrazole or T2)
8.39
8.65–7.23 2.48–2.17
8.92–7.52 2.75–2.47
7.90 (indole or T1)
9.17–7.66 2.78–2.49
9.12–7.70 2.73–2.40
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
3.25–2.52 9.90
(s, 3H, toluidine, CH3) (pyrazole or T2)
9.32–7.64 2.74–2.38 8.43
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
2.70–2.24 9.91
(s, 3H, toluidine, CH3) (pyrazole or T2)
9.30–7.65 2.66–2.37 8.43
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
2.73–1.97 9.90
(s, 3H, toluidine, CH3) (pyrazole or T2)
9.34–7.16 2.73–2.38 8.48
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
4.28–3.84 10.01
(s, 3H, anisidine, CH3) (pyrazole or T2)
9.28–7.08 2.72–2.36 8.44
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
4.32–3.93 9.93
(s, 3H, anisidine, CH3) (pyrazole or T2)
9.34–7.63 2.73–2.41 8.44
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
3.05–2.27 9.08
(s, 3H, toluidine, CH3) (pyrazole or T2)
8.84–7.23 2.46–2.16 7.57
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
2.63–2.12 9.06
(s, 3H, toluidine, CH3) (pyrazole or T2)
8.82–7.23 2.45–2.16 7.57
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
2.57–1.96 9.05
(s, 3H, toluidine, CH3) (pyrazole or T2)
8.85–6.71 2.45–2.16 7.56
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
4.09–3.73 9.07
(s, 3H, anisidine, CH3) (pyrazole or T2)
8.81–6.81 2.45–2.15 7.54
(m, 13H) (s, 3H, pyrazole, CH3) (indole or T1)
4.07–3.77 9.03
(s, 3H, anisidine, CH3) (pyrazole or T2)
8.91–7.21 2.42–2.17 7.58
(m, 13H)
(s, 3H, pyrazole, CH3) 9.32 (pyrazole or T2) (m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
3.44–2.61 9.70
(s, 3H, toluidine, CH3) (pyrazole or T2)
3.28–2.54
(s, 3H, toluidine, CH3)
9.11–7.51 2.72–2.46
7.92 (indole or T1)
9.33–7.63 2.78–2.48
8.35
(m, 13H)
(s, 3H, pyrazole, CH3) 9.30 (pyrazole or T2) (m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
2.80–2.29
(s, 3H, toluidine, CH3) (pyrazole or T2)
2.81–2.40
(s, 3H, toluidine, CH3)
9.09–7.51 2.72–2.45
9.75
7.91 (indole or T1)
9.56–7.88 3.00–2.72
8.58
(m, 13H)
(s, 3H, pyrazole, CH3) 9.29 (pyrazole or T2) (m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
3.00–2.31
(s, 3H, toluidine, CH3) (pyrazole or T2)
2.76–2.23
(s, 3H, toluidine, CH3)
9.14–6.89 2.71–2.46
9.98
3h
3i
7.90 (indole or T1)
9.36–7.08 2.74–2.48
8.35
(m, 13H)
(s, 3H, pyrazole, CH3) 9.31 (pyrazole or T2) (m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
4.29–3.85
(s, 3H, anisidine, CH3) (pyrazole or T2)
4.25–3.82
(s, 3H, anisidine, CH3)
9.09–6.95 2.72–2.44
9.81
7.88 (indole or T1)
9.32–7.03 2.75–2.46
8.32
(m, 13H)
(s, 3H, pyrazole, CH3) 9.26 (pyrazole or T2) (m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
4.28–3.89
(s, 3H, anisidine, CH3) (pyrazole or T2)
4.23–3.85
(s, 3H, anisidine, CH3)
9.19–7.50 2.67–2.46
(m, 13H) (s, 3H, pyrazole, CH3) 9.32 (pyrazole or T2) (m, 13H)
9.73
3j
7.93 (indole or T1)
9.58–7.88 2.99–2.75
8.59
(s, 3H, pyrazole, CH3) (indole or T1)
9.95
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
9.08
9.90
(pyrazole or T2)
(pyrazole or T2)
(pyrazole or T2)
3k
3l
8.81–7.17 2.43–2.17
7.61
9.09–7.39 2.68–2.46
(m, 13H) (s, 3H, pyrazole, CH3) 9.31 (pyrazole or T2) (m, 13H)
7.95 (indole or T1)
9.29–7.60 2.72–2.47
8.39
(s, 3H, pyrazole, CH3) (indole or T1)
9.79
9.28–7.62 2.70–2.38
8.51
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
9.08
(pyrazole or T2)
7.60
9.97
(pyrazole or T2)
8.49
(pyrazole or T2)
8.77–7.22 2.44–2.17
9.04–7.49 2.69–2.46
(m, 13H) (s, 3H, pyrazole, CH3) 9.30 (pyrazole or T2) (m, 13H)
7.94 (indole or T1)
9.28–7.62 2.76–2.50
8.37
(s, 3H, pyrazole, CH3) (indole or T1)
9.80
9.26–7.64 2.72–2.39
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
(m, 13H)
(s, 3H, pyrazole, CH3) (indole or T1)
9.06
9.97
(pyrazole or T2)
(pyrazole or T2)
(pyrazole or T2)
3m 8.84–7.23 2.47–2.18
7.57 (indole or T1) 9.41–7.80 3.02–2.76
(s, 3H, pyrazole, CH3) 9.07 (m, 14H) (s, 3H, pyrazole, CH3) 9.60 (pyrazole or T2) (m, 14H)
(pyrazole or T2)
8.19 (indole or T1)
9.38–7.65 2.80–2.50
8.33
(s, 3H, pyrazole, CH3) (indole or T1)
9.67
9.34–7.69 2.76–2.42
8.40
(m, 14H)
(m, 14H)
(s, 3H, pyrazole, CH3) (indole or T1)
9.88
(pyrazole or T2)
(pyrazole or T2)
T1: hydrazo form of indole.
T2: hydrazo form of pyrazole.

232
Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
Table 4
Sum of electronic and zero-point energies (Hartree/particle) of dyes 3a–3m at DFT (B3LYP).
Dye no.
6-31G(d)
Dipole moment
(Debye)
6-311G(d)
Dipole moment
(Debye)
6-311++G(d,p)
Dipole moment (Debye)
6-31++G(d,p)
Dipole moment
(Debye)
3a
3b
3c
3d
3e
3f
3h
3i
3j
−1513,280578
−1513,293310
−1513,293353
−1348,078702
−1348,083552
−1348, 083983
−1423, 282351
−1423,284339
−1768,388631
−1768,399185
−1768,399362
−1308,793093
4,200
5,906
11,332
6,046
6,045
5,674
5,459
3,939
5,329
5,938
7,547
6,034
−1513,616506
−1513,628682
−1513,628464
−1348,364632
−1348,369924
−1348,370235
−1423,590004
−1423,591897
−1768,694677
−1768,705404
−1768,705552
−1309,071896
4,322
5,903
11,336
6,158
6,139
5,743
5,530
3,956
5,503
6,034
7,684
6,125
−1513, 676437
−1513,688262
−1513,688552
−1348,421208
−1348,426638
−1348,427021
−1423,649863
−1423,651718
−1768,748943
−1768,759108
−1768,759127
−1309,126231
4,757
6,022
11,510
6,039
6,030
5,539
5,372
3,806
5,415
5,794
7,306
5,973
−1513, 369284
−1513,354855
−1513,382283
−1348,162283
−1348,167629
−1348,168033
−1423,369968
−1423,371798
−1768,467661
−1768,478231
−1768,478405
−1308,931903
4,841
5,832
11,662
6,088
6,073
5,601
5,439
3,862
5,437
5,852
7,384
6,029
3k
3l
3m
a
b
c
d
e
f
Fig. 5. The calculated optimized structures of dyes 3a–3m.

Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
233
h
i
j
k
l
m
Fig. 5 (continued).
density. DFT orbitals are formed from basic functions like those used in
SCF or MP2. Most popular DFT method is B3LYP (Becke3-Parameter
method for calculating that part of the molecular energy due to
overlapping orbitals, plus the Lee–Yang–Parr method of accounting for
correlation) [16].
electronic transition energies. Oscillator strengths were deduced from
the dipole transition matrix elements (for singlet states only).
3. Results and discussion
All the calculations were performed by using Gaussian 09.A1 pro-
gram on a personal computer and GaussView 5.0.8 was used for visual-
ization of the structure and simulated vibrational spectra [17]. The
molecular structures of all disazo dyes 3a–3m have been optimized
to the global minima at the levels of using HF and DFT methods with
6-31G(d), 6-311G(d), 6-311++G(d,p) and 6-31++G(d,p) basis sets.
Time-dependent DFT (TDDFT) calculations were then performed with
the same functional and basis set at the optimized geometry to obtain
The selected physical properties of the synthesized dyes 3a–3m
were measured and listed in Table 1.
Tautomerism is significant for areas of chemistry. Especially, the azo-
hydrazone tautomerism is interesting for theoretical studies. Tautomers
have different properties. Azo dyes are mostly in hydrazone form.
Disazo dyes 3a–3m can exist in four possible tautomeric forms, namely
the disazo-enamine form, the hydrazo-azo-enamine form, the azo-
hydrazo-imine and the dishydrazo-imine form as shown in Fig. 3. 1H

234
Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
NMR spectra and FT-IR spectra of dyes are presented in Table 2. 1H NMR
spectra of dyes 3a–3m showed broad peaks at 12.75–8.05 ppm (NH)
of indole or hydrazo form of indole and 13.59–8.72 ppm (NH) of
pyrazole or hydrazo form of pyrazole, respectively. The other δ values
of 2.70–2.37 ppm (CH3) and 8.96–6.92 ppm (aromatic H) were
recorded. 3d–3f showed broad peaks at 2.20–1.18 ppm (CH3) of tolui-
dine. 3h and 3i showed broad peaks at 3.94–3.85 ppm (OCH3) of
anisidine. 1H NMR spectra of dyes 3a and 3b are illustrated in Fig. 4.
1H NMR chemical shift values have been obtained by using the gauge in-
cluding atomic orbital (GIAO)–DFT method at the same functional and
basis set and listed in Table 3. Comparing experimental data with
theoretical NMR chemical shifts provides practical information on the
chemical structures of compounds. The FT-IR spectra of dyes 3a–3m
showed imino (NH) band at 3350–3040 cm−1, aromatic (Ar–H) band
at 2975–2886 cm−1 and azo (N_N) band at 1570–1520 cm−1 were
recorded. There is a generally excellent agreement between the
theoretical and experimental data, with the differences in only a few
wavenumbers. These suggest that these disazo dyes are predominantly
in one of the hydrazo-azo-enamine or the azo-hydrazo-imine forms as
opposed to the disazo-enamine and dishydrazo-imine forms, in the
solid state.
UV spectrum analyses of 3a–3m have been investigated experimen-
tally and theoretically. Absorption spectra of dyes 3a and 3b are illus-
trated in Fig. 6. The UV spectrum of compounds was measured in six
different solvents acetonitrile, acetic acid, methanol, chloroform, DMF
and DMSO. The absorption maxima of the compounds have been
found by using Self-Consistent Field (SCF) method at 6-31G(d), 6-
311G(d), 6-311++G(d,p), and 6-31++G(d,p) level and listed in
Table 6. The UV–vis absorption spectra of dyes 3a–3m were recorded
in the range of λ between 350 and 600 nm, using a variety of solvents
in concentrations (1 × 10−6–1 × 10−8 M). The visible absorption spec-
tra of the dyes did not correlate with the polarity of solvent. Single max-
imum is seen in the spectra of the compound 3a–3m in all used
solvents. When compared with λmax values of obtained disazo dyes,
λ
max of dyes in DMF showed more bathochromic shifts than λmax of
dyes in the other solvents except for 3a, h and l. λmax of 3c does not sig-
nificantly change in all used solvents. Hypsochromic shift is seen in the
spectra of compound 3d in methanol. The obtained disazo dyes gave a
single dominant absorption peak without a shoulder in all used sol-
vents. It can be said that the maximum values in all solvents are very
close to each other and don't change much.
Theoretically computed thermo dynamical parameters such as the
SCF energy, zero-point vibrational energies (ZPVE), the entropy, the
heat capacity, rotational constants and dipole moment have been pre-
sented in Table 7. Based on the vibrational analysis at B3LYP/6-
311++G(d,p) level, the standard statistical thermodynamic functions:
heat capacity, entropy and enthalpy changes for the compound studied
were obtained from the theoretical harmonic frequencies.
Calculated energies and energy difference for all basis sets of 3a–3m
were determined by B3LYP and different basis sets were presented in
Table 4. The basis set size effect on the calculated energies. There is a lit-
tle difference between basis sets. Using the basis sets of larger sizes
gives rise to increases in the differences between the calculated energies
of 3a–3m.
The optimized structures of 3a–3m were shown in Fig. 5 with num-
bering of the atoms. The vibrational frequencies and optimized structure
parameters of disazo dye 3a have been calculated by using DFT methods
at 6-31G(d), 6-311G(d), 6-311++G(d,p), and 6-31++G(d,p) basis set
level and listed in Table 5.
4. Conclusions
In this work, we performed the experimental and theoretical vibra-
tional analysis of 3a–3m. A series of twelve novel containing indole
Table 5
Calculated vibrational frequencies, bond length and bond angle of dye 3a.
Parameters
(stretching)
Calculated
Calculated bond length
6-31G(d,p)
Parameters
(bending)
Calculated
Calculated bond angle
6-31G(d,p)
frequencies
frequencies
(cm−1
)
(cm−1
)
DFT
HF
DFT
HF
DFT
HF
DFT
HF
N(6)–H(4)
3662
3647
3238
3122
1414
3213
3094
3040
3167
3190
3163
3181
1058
1414
1085
380
1431
1618
1653
1304
1610
1474
1014
1639
1304
1085
1520
1035
1561
1613
1316
3915
3898
3403
3269
1504
3368
3246
3187
3320
3352
3322
3341
1129
1380
1777
1209
1803
1793
1803
1793
1777
1315
1793
1594
1758
1425
1639
1765
1437
1199
759
1.007670
1.007799
1.079912
1.091034
1.363628
1.081375
1.092540
1.091034
1.084365
1.083240
1.084669
1.084141
1.394474
1.324513
1.409257
1.478871
1.279077
1.401708
1.391983
1.391280
1.391799
1.389268
1.391086
1.390852
1.404862
1.350210
1.390639
1.404318
1.407623
1.394034
1.372540
0.991870
0.992305
1.070810
1.082589
1.377267
1.073132
1.083787
1.082589
1.075678
1.074222
1.075538
1.075243
1.384293
1.296099
1.375574
1.467019
1.226644
1.397484
1.388772
1.377582
1.382879
1.382818
1.384320
1.383770
1.391699
1.329226
1.377867
1.400217
1.371410
1.384910
1.385201
C(3)–N(5)–N(6)
794
632
1109
948
1567
674
946
29
410
106.11
120.14
118.40
112.55
122.01
115.79
124.84
121.62
109.54
121.10
116.03
106.59
109.44
126.15
118.96
119.73
119.06
119.37
120.16
117.64
116.22
125.29
120.96
121.17
121.51
117.07
119.81
120.12
119.67
120.39
106.75
120.07
118.46
112.89
122.55
115.90
125.17
121.49
109.49
121.12
116.04
107.38
109.38
125.45
119.21
119.81
119.29
119.57
120.20
117.65
116.67
125.31
121.03
121.02
121.31
117.18
119.62
120.24
119.55
120.69
N(18)–H(49)
C(20)–H(24)
C(7)–H(8)
N(12)–C(16)
C(39)–H(43)
C(7)–H(9)
C(38)–C(40)–C(44)
C(15)–C(20)–C(23)
C(2)–N(11)–N(12)
C(2)–C(1)–N(14)
N(50)–C(29)–C(28)
H(49)–N(18)–C(48)
H(22)–C(19)–C(48)
H(8)–C(7)–H(9)
593
1497
1240
1174
1431
593
374
1644
1391
1596
946
C(7)–H(8)
C(19)–H(22)
C(27)–H(33)
C(38)–H(41)
C(42)–H(46)
C(27)–C(32)
N(5)–C(3)
C(19)–C(21)–C(23)
C(31)–C(30)–N(13)
H(9)–C(7)–H(10)
H(8)–C(7)–H(10)
N(6)–C(2)–N(11)
H(26)–C(23)–C(20)
H(33)–C(27)–C(28)
H(34)–C(28)–C(29)
H(41)–C(38)–C(40)
H(45)–C(40)–C(44)
O(51)–N(50)–C(29)
C(1)–N(14)–N(13)
O(52)–N(50)–O(51)
C(17)–C(16)–N(12)
C(17)–C(37)–C(39)
C(20)–C(23)–C(21)
C(21)–C(19)–C(48)
C(29)–C(28)–C(27)
C(27)–C(32)–C(31)
C(28)–C(27)–C(32)
C(7)–C(3)–N(5)
496
639
1474
1431
148
1174
1338
1497
1639
1185
593
148
862
150
380
573
884
585
916
803
585
1602
1567
29
1391
1596
1657
1793
1793
959
639
759
696
363
639
616
616
759
1017
592
C(1)–C(2)
N(50)–C(29)
N(11)–N(12)
C(15)–C(20)
C(19)–C(48)
C(19)–C(21)
C(27)–C(28)
C(31)–C(32)
C(38)–C(40)
C(39)–C(42)
C(37)–C(39)
N(6)–C(2)
C(20)–C(23)
C(21)–C(23)
C(16)–C(17)
C(40)–C(44)
N(14)–C(1)

Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
235
Fig. 6. Absorption spectra of dyes 3a and 3b.
cycle disperse azo dyes 3a–3m were synthesized in reasonably good
yields. The newly synthesized compounds were characterized by 1H
NMR, mass spectrometry, IR studies and elemental analysis. Also, ab-
sorption ability of these compounds, solvent influence on the wave-
length of maximum absorption, was studied. The visible absorption
spectra of the dyes did not correlate with the polarity of solvent. In ad-
dition, theoretical studies of novel disazo dyes were evaluated. The vibra-
tional frequencies, optimized molecular structures and corresponding
vibrational assignments of heterocyclic disazo dyes (3a–3m) have been
calculated using HF and DFT (B3LYP) methods at 6-31G(d), 6-311G(d),
6-311++G(d,p) and 6-31++G(d,p) basis set level. The calculated
wavenumbers were compared with experimental FT-IR. We performed
1H chemical shifts of 3a–3m. The positions of hydrogen atoms of mole-
cules were determined by means of computed 1H chemical shifts. Also,
UV spectrum analyses of 3a–3m have been investigated theoretically.
The data were compared with the experimental results. There is general-
ly an excellent agreement between the theoretical and experimental
data, with the differences in only a few values.
Table 6
Influence of solvent on λmax (nm) of dyes 3a–3m.
Experimental
B3LYP/6-311++g(d,p)
Acetonitrile
Acetic acid
Methanol
Chloroform
DMF
DMSO
Acetonitrile
Acetic acid
Methanol
Chloroform
DMF
DMSO
3a
3b
3c
3d
3e
3f
3h
3i
3j
486
485
486
465
465
465
475
466
473
466
479
464
466
485
485
462
465
465
465
465
466
466
465
465
475
478
486
422
465
460
464
465
464
468
466
465
486
485
486
463
461
465
468
441
466
465
475
466
485
486
486
474
466
486
474
486
486
487
475
469
485
476
486
465
466
465
465
466
465
465
465
465
515
495
543
506
492
490
491
495
506
492
495
490
512
496
538
513
498
495
496
496
512
495
497
496
522
497
547
511
496
494
495
497
513
495
497
495
513
500
538
515
500
497
499
499
515
497
499
498
517
498
545
507
492
491
492
498
507
494
497
490
517
497
545
506
492
491
492
498
507
494
496
490
3k
3l
3m

236
Ç. Karabacak, O. Dilek / Journal of Molecular Liquids 199 (2014) 227–236
Acknowledgments
The authors would like to thank Dr. Tahir Tilki and Dr. Izzet Kara for
technical and theoretical support. The authors are grateful to PAUBAP
(Project No. 2012BSP004) and TUBITAK (Project No. 107T606) for
their financial support. Computation has been performed using
TUBITAK/ULAKBIM clusters.
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