Phenylazoindole dyes 2: The molecular structure characterizations of new phenylazo indoles derived from 1,2-dimethylindole

Article abstract of DOI:10.1016/j.dyepig.2013.11.019

In this study, five new phenylazo indoles derived from 1,2-dimethylindole were synthesized and characterized to evaluate the substituent effects on the molecular structures and absorption spectra. Theoretical calculations were carried out by density funct

Full text of DOI:10.1016/j.dyepig.2013.11.019

Dyes and Pigments 103 (2014) 62e70
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Phenylazoindole dyes 2: The molecular structure characterizations
of new phenylazo indoles derived from 1,2-dimethylindole
a
b
a
c
d
ꢀ
Banu Babür , Nurgül Seferoglu , Ebru Aktan , Tuncer Hökelek , Ertan S¸ ahin ,
a,
*
ꢀ
Zeynel Seferoglu
a Gazi University, Department of Chemistry, 06500 Ankara, Turkey
b Gazi University, Advanced Technologies, 06500 Ankara, Turkey
c Hacettepe University, Department of Physics, 06800 Beytepe, Ankara, Turkey
d Atatürk University, Department of Chemistry, Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, five new phenylazo indoles derived from 1,2-dimethylindole were synthesized and
characterized to evaluate the substituent effects on the molecular structures and absorption spectra.
Theoretical calculations were carried out by density functional theory. The experimental and theo-
retical results are compared. X-ray single-crystal diffraction analyses reveal that the dyes have similar
planar molecular conformation between azo and aromatic/heteroaromatic ring units but dissimilar
crystal packing. The analysis of the electronic spectra showed that the electron-withdrawing groups
(eCl and eCN) were more effective than the electron-donating groups (eCH3 and eOCH3). Dyes
containing electron-donating groups do not show significant changes relative to the parent dye,
whereas the absorption maxima move to longer wavelengths for dyes containing electron-
withdrawing groups . In addition, the absorption maxima exhibit the little bathochromic shifts for
each dye with the increasing dielectric constants of the solvents.
Received 14 July 2013
Received in revised form
18 November 2013
Accepted 19 November 2013
Available online 27 November 2013
Keywords:
Azo dyes
Phenylazo indoles
X-ray
DFT
Substituent effect
UVevis
Ó 2013 Published by Elsevier Ltd.
1. Introduction
1,2-dimethyl-1H-indole (dye 1). In our ongoing study, the syn-
theses of a new series, phenylazo-1,2-dimethylindole, containing
It is well known that azo dyes have one or more eN]Ne
groups, which link two aromatic/heteroaromatic rings and are the
most widely used class of dyes [1e3]. In recent years, much
attention has been directed to the investigations of the chemical
and physical properties of azo dyes, due to their biological and
physicochemical properties [1e9] as well as their potential wide
applications in many other fields [10e14].
Although there is an extensive literature on azo dyes, it is
very important to synthesize and characterize new azo dyes
experimentally and also theoretically using the computational
method to provide guidance for further studies. The dyes based
on heterocyclic coupling components such as indoles are
commercially important azo dyes [1]. In earlier studies [15,16],
we have reported the tautomeric properties of some phenyl-
azoindole dyes and X-ray crystal structure of 3-phenyldiazenyl-
the electron-withdrawing (eCN and eCl) and electron-donating
(eCH3 and eOCH3) groups at para position of the phenyl ring are
reported. The effects of the substituent groups on the ground-
state geometries, energies of molecular orbitals and absorption
wavelengths are investigated by using the spectroscopic and
computational techniques. This study is important since it pro-
vides the first syntheses and characterizations of the five new
azo dyes by using the spectroscopic techniques. In addition, the
crystal structure of each dye was also obtained. In calculations,
the density functional theory (DFT) method was employed to
obtain the ground state geometries of all dyes and time-
dependent DFT (TD-DFT) was used to study the absorption
spectra in gas phase and in solution. According to the experi-
mental and theoretical results, the discussion of the influences
produced by the substituent groups and by the different solvents
on the absorption wavelenghts, the highest occupied and lowest
unoccupied molecular orbitals (HOMOeLUMO) and also molec-
ular electrostatic maps (MEP) are given with respect to our
reference compound (dye 1, Fig. 1).
* Corresponding author. Tel.: þ90 312 2021525; fax: þ90 312 2122279.
ꢀ
E-mail address: znseferoglu@gazi.edu.tr (Z. Seferoglu).
0143-7208/$ e see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.dyepig.2013.11.019

B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
63
X
NH2
1.X=H
N
NaNO2
HCl
2.X=CH3
3.X=OCH3
4.X=Cl
N
CH3
N
CH3
CH3
X
N
5.X=CN
CH3
Fig. 1. Synthetic pathway and structure of compounds.
2. Experimental
1H, J1 ¼ 7.37 Hz, J2 ¼ 1.05 Hz), 3.74 (s, 3H, eNCH3), 2.82 (s, 3H, e
CH3), HRMS (Mþ) calcd for C16H16N3 250.1344; found, 250.1343.
2.1. Material and methods
2.2.2. Preparation of (E)-3-(4-Methylphenyldiazenyl)-1,2-dimethyl-
1H-indole (2)
The chemicals used in the syntheses of all compounds were
from the Aldrich Chemical Company and used without further
purification. The solvents were used of spectroscopic grade. IR
spectra were recorded on a Mattson 1000 FT-IR spectrophotometer
The dye was obtained from p-toluidine and 1,2-dimethylindole
as orange crystals (0.465 g, 88% yield; m.p: 145 ꢁC) FT-IR (KBr)
٧
max: 3024 (aromatic CeH), 2918 (aliphatic CeH), 1598, 1535, 1472,
in KBr (
Spectrospin Avance DPX 300 Ultra-Shield in DMSO-d6. Chemical
shifts are expressed in units (ppm). Ultravioletevisible (UVevis)
n
, are in cmꢀ1). H NMR spectra were recorded on a Bruker-
1448 (C]C), 1385 (N]N) cmꢀ1; 1H NMR (DMSO-d6):
d
8.40 (d, 1H,
J1 ¼ 8.04 Hz), 7.78 (d, 2H, J1 ¼ 8.87 Hz), 7.55 (d, 1H, J1 ¼ 7.90 Hz),
7.30e7.20 (m, 2H), 7.05 (d, 2H, J1 ¼ 8.89 Hz), 3.70 (s, 3H, eNCH3),
2.60 (s, 3H, eCH3), 2.38 (s, 3H, eCH3), HRMS (Mþ) calcd for
d
absorption spectra were recorded on Analytik Jena Specord 200
spectrophotometer at the wavelength of maximum absorption
C17H18N3 264.1501; found, 264.1507.
(lmax, in nm) in the solvents specified. Mass spectra were recorded
on a Waters-LCT-Premier-XE-LTOF (TOF-MS) instruments; in m/z
(rel. %). The X-ray data were recorded in the Department of
Chemistry, Atatürk University, Erzurum, Turkey.
2.2.3. Preparation of (E)-3-(4-Methoxyphenyldiazenyl)-1,2-
dimethyl-1H-indole (3)
The dye was obtained from p-anisidine and 1,2-dimethylindole
as yellow crystals (0.504 g, 90% yield; m.p: 105 ꢁC) FT-IR (KBr) ٧max
:
3050 (aromatic CeH), 2932e2833 (aliphatic CeH), 1598, 1577, 1537,
2.2. Preparation of dyes (1e5)
1495, 1455 (C]C), 1387 (N]N), 1245 (CeO) cmꢀ1; 1H NMR (DMSO-
d6):
d
8.40 (d, 1H, J1 ¼7.25 Hz), 7.70 (d, 2H, J1 ¼ 8.21 Hz), 7.56 (d, 1H,
Various carbocyclic amines can be diazotized with HCl and
NaNO2. A typical procedure of diazotizing and coupling is described
below using aniline and 1,2-dimethylindole; all other compounds
were prepared in a similar manner. The yields of the dyes are in the
range of 76e90%. The obtained compounds were purified by crys-
tallization using ethanol by slow evaporation in several days, and
then analyzed.
J1 ¼7.85 Hz), 7.35 (d, 2H, J1 ¼8.18 Hz), 7.30e7.20 (m, 2H), 3.85 (s, 3H,
eOCH3), 3.78 (s, 3H, eNCH3), 2.80 (s, 3H, eCH3), HRMS (Mþ) calcd
for C17H18N3O 280.1455; found, 280.1453.
2.2.4. Preparation of (E)-3-(4-Chlorophenyldiazenyl)-1,2-dimethyl-
1H-indole (4)
The dye was obtained from p-chloroaniline and 1,2-
dimethylindole as yellow crystals (0.436 g, 82% yield; m.p:
137 ꢁC) FT-IR (KBr) ٧max: 3047 (aromatic CeH), 2931 (aliphatic Ce
2.2.1. Preparation of (E)-3-phenyldiazenyl-1,2-dimethyl-1H-indole
(1)
H), 1531, 1473, 1451, 1404 (C]C), 1380 (N]N) cmꢀ1 1H NMR
;
Aniline (0.18 mL, 2.0 mmol) was dissolved in concentrated HCl
(1.5 mL, % 36 w/w) and water (4.0 mL). The solution was cooled in
an ice-salt bath and a cold solution of NaNO2 (0.15 g, 2 mmol) in
water (3.0 mL) was added dropwise with stirring. The mixture was
stirred for an additional 1 h at 273 K. Excess nitrous acid was
destroyed by the addition of urea. The resulting diazonium salt was
cooled in a salt/ice mixture. 1,2-dimethylindole (0.29 g, 2.0 mmol)
was dissolved in a mixture of acetic acid and propionic acid solution
(3.0 : 1.8 mL) and cooled in an ice bath. Then, cold diazonium so-
lution was added to this cooled solution by stirring in a dropwise
manner. The solution was stirred at 273e278 K for 1 h. The pH of
the reaction mixture was maintained at 4e6 by the simultaneous
addition of saturated sodium carbonate solution. The mixture was
stirred for a further 1 h at room temperature. The resulting solid
was filtered, washed with cold water, and then dried. Recrystalli-
zation from ethanol gave yellow crystals (0.425 g, 85% yield; m.p:
125 ꢁC) FT-IR (KBr) ٧max: 3055 (aromatic CeH), 2915 (aliphatic Ce
H), 1534, 1476,1446 (C]C), 1387 (N]N) cmꢀ1; 1H NMR (DMSO-d6):
(DMSO-d6):
d
8.45 (d,1H, J1 ¼7.18 Hz), 7.89 (d, 2H, J1 ¼8.68 Hz), 7.64
(d, 1H, J1 ¼ 8.90 Hz), 7.62 (d, 2H, J1 ¼ 8.71 Hz), 7.37e7.28 (m, 2H),
3.85 (s, 3H, eNCH3), 2.82 (s, 3H, eCH3), HRMS (Mþ) calcd for
C16H15N3CI 284.0955; found, 284.0955.
2.2.5. Preparation of (E)-3-(4-Cyanophenyldiazenyl)-1,2-dimethyl-
1H-indole (5)
The dye was obtained from p-aminobenzonitrile and 1,2-
dimethylindole as brown crystals (0.418 g, 76% yield; m.p: 152 ꢁC)
FT-IR (KBr) ٧max: 3050 (aromatic CeH), 2910 (aliphatic CeH), 2224
(C^N), 1596, 1529, 1474, 1409 (C]C), 1394 (N]N) cmꢀ1 1H NMR
;
(DMSO-d6):
d
8.41 (dd, 1H, J1 ¼ 8.13 Hz, J2 ¼ 1.59 Hz), 7.94 (m, 4H),
7.60 (d, 1H, J1 ¼7.45 Hz), 7.35 (td, 1H, J1 ¼7.26 Hz, J2 ¼ 1.42 Hz), 7.25
(td, 1H, J1 ¼7.25 Hz, J2 ¼ 1.12 Hz), 3.70 (s, 3H, eNCH3), 2.60 (s, 3H, e
CH3), HRMS (Mþ) calcd for C17H15N4 275.1297; found, 275.1295.
2.3. Computational study
d
8.39 (dd, 1H, J1 ¼ 7.80 Hz, J2 ¼ 1.11 Hz), 7.82 (dd, 2H, J1 ¼ 8.10 Hz,
J2 ¼ 1.13 Hz), 7.58 (d, 1H, J1 ¼ 7.59 Hz), 7.51 (t, 2H, J1 ¼ 8.01 Hz), 7.38
(t, 1H, J1 ¼ 7.28 Hz), 7.29 (td, 1H, J1 ¼ 7.25 Hz, J2 ¼ 1.33 Hz), 7.25 (td,
The geometries of all the compounds (dyes 1e5) has been fully
optimized in the ground state at the B3LYP/6-311þG(p,d)

64
B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
computational level [17e19]. The integral equation formalism of the
polarizable continium model (PCM) was employed [20,21]. The
vibrational frequencies were calculated at the same theoretical level
to confirm that all optimized ground configurations had no imagi-
nary frequencies and the ground-state minima were on potential
energy surfaces. Absorption spectra were computed as vertical
electronic excitations from the ground-state minima by using the
time-dependent density functional theory (TD-DFT) [22]. All cal-
culations were performed with the Gaussian 09 program [23].
fibers, the coloring mechanism and other related technical perfor-
mance [26e28].
The asymmetric units of dyes 2, 4 and 5 contain only one
molecule (Fig. 2(a),(c) and (d)), while the asymmetric unit of dye 3
contains two crystallographically independent molecules
(Fig. 2(b)). Selected bond lengths and angles together with the
selected torsion angles are given in Table 2. An examination of the
deviations from the least-square mean planes through the indi-
vidual rings showed that all of the rings are planar. The indole ring
systems were planar with dihedral angles of 0.76(13)ꢁ (for dye 2),
3.19(15)ꢁ and 0.72(15)ꢁ (for dye 3), 2.54(13)ꢁ (for dye 4) and
1.04(18)ꢁ (for dye 5) between rings A (N1/C1eC3/C8) and B (C3eC8)
(for dyes 2, 3, 4 and 5) and between rings A0 (N10/C10eC30/C80) and
B0 (C30eC80) (for dye 3). In the closely related compounds, 3-(4-
chlorophenyldiazenyl)-1-methyl-2-phenyl-1H-indole 6 [29], N-{4-
2.4. Crystallography
X-ray diffraction data of the azo dyes 2e5 were collected for
comparison of the structural results with the corresponding ones
obtained from the theoretical calculations. Diffraction data collec-
[(2-phenyl-1H-indol-3-yl)-diazenyl]-phenyl}acetamide
7
[30],
tions were performed on a Rigaku R-AXIS RAPID-S diffractometer
ꢁ
ethyl[2-(2-phenyl-1H-indol-3-yldiazenyl)-1,3-thiazol-4-yl] acetate
8 [31], 1,2-dimethyl-3-(pyridin-3-yldiazenyl)-1H-indole 9 [32] and
1,2-dimethyl-3-(5-methylisoxazol-3- yldiazenyl)-1H-indole 10
[33], the observed A/B and A0/B0 dihedral angles were 1.56(11)ꢁ and
0.77(12)ꢁ in 6 1.63(14)ꢁ in 7, 0.99(10) in 8, 2.71(7)ꢁ in 9 and
0.45(11)ꢁ in 10. The orientations of the phenyl rings C (C11eC16)
and C0(C110eC160) with respect to the planar indole ring systems
might be described by the dihedral angles of 12.97(7)ꢁ (for dye 2),
15.80(11)ꢁ and 19.50(13)ꢁ (for dye 3), 11.83(10)ꢁ (for dye 4), and
4.18(8)ꢁ (for dye 5). The partial packing diagrams are shown in
Fig. 3(a)e(d), for dyes 2, 3, 4 and 5, respectively. The bond lengths of
using Mo K
a
radiation (
l
¼ 0.71073 A) at T ¼ 294 K. Integration of
the intensities, correction for Lorentz and polarization effects and
cell refinement were performed using CrystalClear (Rigaku/MSC
Inc., 2005) software [24]. The structures were analyzed using a
combination of direct and difference Fourier methods provided by
SHELXS97 [25] and were refined as full-matrix least squares against
F2 using all data by SHELXL97 [25] computer programs; all non-
hydrogen atoms were refined anisotropically. H atoms were posi-
tioned geometrically at distances of 0.93 (for aromatic CH) and
ꢁ
0.96 A (for methyl groups) from the parent C atoms; a riding model
was used during the refinement processes and the Uiso(H) values
were constrained to be xUeq(carrier atom), where x ¼ 1.5 for methyl
H, and x ¼ 1.2 for aromatic H atoms. The final difference Fourier
maps showed no peaks of chemical significance. Crystal data and
details of the structure determination for the compounds are
summarized in Table 1.
ꢁ
azo units (N2eN3) are in the range of 1.272(4)e1.285(5)A corre-
sponding to the double-bond character.
In the crystal packing of azo 2e5 dyes,
p.p stacking in-
teractions are found between the phenyl rings and the indole rings
of neighboring molecules with the centroidecentroid separations
ꢁ
of 3.626(2)- 3.852(2) A. There also exist weak CeH.
p interactions
in dyes 2e5 (Table 3). In dye 3, there are no classical intermolecular
hydrogen bonds but CeH.O short contacts (Table 3) describe a
cyclic tetramer (Fig. 3(b)).
3. Results and discussion
3.1. Description of the crystal structures
The single-crystal X-ray structural determinations of dye mol-
ecules are of great significance because they reveal their molecular
conformations, packing fashions and supramolecular interactions,
which will help to understand the interactions between dyes and
3.2. Geometric parameters
The optimized structure parameters by DFT method with B3LYP
functional are listed in Table 2, which are in accordance with the
Table 1
Crystallographic details for dyes 2, 3, 4 and 5.
Dyes
2
3
4
5
Chemical formula
FW/g molꢀ1
C17H17N3
263.34
C34H34N6O2
558.67
C16H14N3Cl
591.9
C17H17N4
274.32
Crystal System
Space group
monoclinic
P21/c
7.3848(3)
15.2260 (5)
12.8781(4)
90
93.31(3)
90
1445.61(10)
4
1.210
triclinic
P e1
7.267(5)
10.695(5)
20.349(4)
98.943(5)
90.630(5)
106.469(5)
1495.7(13)
2
1.241
0.80
592
0.30 ꢂ 0.25 ꢂ 0.15
4.20e52.84ꢁ
31015
monoclinic
P21/c
7.3264(3)
15.2210(4)
12.8722(3)
90
92.21(2)
90
1434.38(8)
4
1.31
0.259
592
0.24 ꢂ 0.19 ꢂ 0.12
2.7e54.6ꢁ
24551
monoclinic
P21/c
8.3501(2)
12.8232(3)
14.2205(4)
90
102.674(2)
90
1485.56(7)
4
1.227
0.076
576
0.35 ꢂ 0.20 ꢂ 0.15
4.32e53.42ꢁ
30583
ꢁ
a/A
ꢁ
b/A
ꢁ
c/A
ꢁ
ꢁ
a
/
b
/
ꢁ
g
/
3
ꢁ
V/A
Z
rcalcmg/mm3
m
(Mo-K
F(000)
Crystal size/mm3
range for data collection
a
)/mmꢀ1
0.73
560
0.35 ꢂ 0.22 ꢂ 0.20
4.14e52.84ꢁ
29717
2
Q
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
2960[R(int) ¼ 0.076]
2960/0/184
0.981
6106[R(int) ¼ 0.087]
6106/0/385
0.996
2984[R(int) ¼ 0.103]
2984/0/184
1.19
3071[R(int) ¼ 0.084]
3071/0/192
1.051
Final R indexes [I ꢃ 2
s
(I)]
R1 ¼ 0.0752, wR2 ¼ 0.2053
R1 ¼ 0.0809, wR2 ¼ 0.1868
R1 ¼ 0.093, wR2 ¼ 0.232
R1 ¼ 0.0715, wR2 ¼ 0.1820
ꢁꢀ3
Largest diff. peak/hole/e A
0.202/-0.290
0.167/-0.207
0.366/0.552
0.197/-0.187

B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
65
Fig. 2. An ORTEP [38] drawing with the atom-numbering scheme for (a) dye2, (b) dye3, (c) dye4, (d) dye5.
atom numbering scheme given in Fig. 2, and they are compared
3.3. Spectral characterizations
with experimental results.
N2]N3 bond lengths are identified by X-ray between 1.272 and
The theoretical and experimental absorption wavelenghts are
obtained in various solvents having different dielectric constants (
such as DMSO ( ¼ 6.17 Debye) and
¼ 46.45 Debye), acetic acid (
chloroform (
¼ 4.81 Debye). The absorption spectra of dyes 1e5
were recorded over the range of (300e700) nm using a variety of
ꢁ
ꢁ
1.184 A and by B3LYP between 1.265 and 1.269 A. All of the
computed N2]N3 bonds are slightly shorter than the experimental
ones. The dyes exist in azo form because they have no tautomeric
hydrogen. Kelemen et al. reported that N]N bond is between 1.20
3
)
3
3
3
l
and 1.28 A in azo tautomers [34]. Geometric parameters for these
solvents in concentrations 10ꢀ6e10ꢀ8 M. In calculations, the ab-
sorption spectra of dyes were calculated at the optimized structure
of the ground state in each solvents using the PCM model linked to
TD-DFT (B3LYP) with the 6-311þG(d,p). The obtained results are
given in Table 4. As can be seen in Table 4, the dyes have strong
ꢁ
azo dyes agree with the corresponding values in our previously
reported studies of indole azo dyes [32,33]. We have identified N]
N bond length for 1,2-dimethyl-3-(pyridin-3-yldiazenyl)-1H-indole
ꢁ
ꢁ
[32] by X-ray as 1.276 A and by B3LYP as 1.272 A and for 1,2-
dimethyl-3-(5-methylisoxazol-3-yldiazenyl)-1H-indole [33] by X-
ray as 1.281 A and B3LYP as 1.269 A. The calculated bond lengths of
single absorption bands, which are assigned to the nep* transitions
ꢁ
ꢁ
from the indole ring to the azo unit in compounds in all solvents.
However, for dyes (1e3) in acetic acid the additional strong bands
are observed at 437, 448 and 466 nm, which can be assigned to the
protonated species for dyes 1, 2 and 3, respectively. Protonation
the N3eC1 bonds in dyes are estimated in the range of 1.374e
ꢁ
1.418 A and they are shorter than the experimental values (1.423e
ꢁ
1.440 A). The errors of bond lengths between the calculated results
ꢁ
and the X-ray data are less than 0.032 A, which corresponds to the
takes place on the b-nitrogen atom of the azo group (Fig. 4), and as a
C11eC12 bond length for dye 5. It is known that large deviations
from experimental CeH bond lengths may arises from the low
scattering factors of hydrogen atoms in the X-ray diffraction ex-
periments. Therefore the discussion of CeH bond length was not
given in here.
The optimized structures of these molecules are nearly planar.
The calculated C1eN2eN3eC11 values of dyes are 180ꢁ, and the
corresponding experimental values lie between 173 and 180ꢁ. The
highest difference between X-ray and calculated angular values
corresponds to the N2eN3eC11 bond angle for dye 3 as 2.7ꢁ.
result a migration of electrons occurs from the electron-rich phenyl
ring to the azo group and the absorption band is seen at a longer
wavelength. For dyes 4 and 5, the donor properties of b-nitrogen
atom of the azo group is decreased, because of the electron-
withdrawing groups located at the para position of the phenyl
ring, and consequently an additional second band corresponding to
the protonation is not observed. The calculated absorption bands at
387 nm with (oscillator strength f) f ¼ 0.92, 389 nm with f ¼ 1.00
and 396 nm with f ¼ 1.05 are assigned to the first bands at 385, 385
and 384 nm for dyes 1e3, respectively.

66
B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
Table 2
ꢁ
ꢁ
ꢁ
Selected bond lengths (A) and angles ( ) with the selected torsion angles ( ) for dyes 1e5. The calculated values are for gas phase.
1
2
3
4
5
Exp.a
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Unprimed
Primed
Bond lengths
O1 e C14
O1 e C17
N1 e C2
N1 e C3
N1 e C9
N2 e N3
N2 e C1
N3 e C11
1.370(5)
1.428(5)
1.366(5)
1.375(6)
1.465(5)
1.284(5)
1.384(5) 1.382(5)
1.434(5)
1.376(5)
1.418(5)
1.361(5)
1.376(6)
1.455(5)
1.273(4)
1.378
1.363
1.421
1.375
1.393
1.451
1.363 (3)
1.388 (3)
1.457 (3)
1.279 (3)
1.382 (3)
1.429 (3)
1.373
1.366 (4)
1.386(4)
1.458(4)
1.272(4)
1.382(4)
1.437(4)
1.374
1.360(5)
1.388(6)
1.477(6)
1.275(5)
1.374
1.371
1.351(3)
1.389(3)
1.456(3)
1.275(3)
1.368
1.394
1.451
1.265
1.376
1.418
1.394
1.451
1.265
1.377
1.416
1.395
1.452
1.266
1.397
1.453
1.269
1.265
1.313(7)
1.413
1.374(3) 1.369
1.423(5)
1.433(6)
1.374
1.440(3)
1.413
1.156
1.399
1.450
1.489
1.393
1.414
1.403
1.392
1.400
1.402
1.406
1.387
1.403
1.407
1.429
N4 e C17
1.133(4)
1.394(4)
1.434(3)
1.478(3)
1.394(4)
1.408(4)
1.395(5)
1.387(4)
1.400(4)
1.371(4)
1.374(4)
1.367(4)
1.381(4)
1.379(4)
1.446(4)
C1 e C2
C1 e C8
C2 e C10
C3 e C4
C3 e C8
C5 e C6
C6 e C7
C7 e C8
C11 e C12
C11 e C16
C12 e C13
C13 e C14
C14 e C15
C14 e C17
C14eCl1
1.390 (4)
1.442 (4)
1.482 (4)
1.382 (4)
1.415 (3)
1.384 (4)
1.378 (4)
1.393 (4)
1.397 (4)
1.387 (4)
1.381 (4)
1.381 (5)
1.380 (5)
1.396
1.449
1.489
1.394
1.415
1.403
1.391
1.401
1.400
1.404
1.392
1.394
1.398
1.379(4)
1.442(5)
1.478(4)
1.389(5)
1.410(4)
1.384(5)
1.375(5)
1.396(4)
1.377(5)
1.393(5)
1.389(5)
1.372(5)
1.388(5)
1.508(5)
1.394
1.449
1.489
1.394
1.416
1.404
1.391
1.401
1.399
1.405
1.392
1.397
1.404
1.509
1.383(6)
1.439(6)
1.494(6)
1.398(6)
1.410(6)
1.390(7)
1.366(6)
1.393(6)
1.391(6)
1.377(6)
1.375(6)
1.394(6)
1.375(6)
1.383(6)
1.437(6)
1.481(6)
1.387(6)
1.406(6)
1.374(7)
1.393(6)
1.391(6)
1.388(5)
1.384(5)
1.372(6)
1.389(6)
1.369(6)
1.394
1.449
1.489
1.394
1.416
1.404
1.391
1.401
1.408
1.396
1.381
1.405
1.397
1.415(6)
1.458(7)
1.496(6)
1.421(5)
1.403(5)
1.404(6)
1.390(5)
1.421(7)
1.393(6)
1.336(5)
1.368(6)
1.375(6)
1.426(5)
1.396
1.450
1.490
1.393
1.415
1.403
1.391
1.400
1.400
1.404
1.391
1.391
1.395
1.760
Bond angles
C2eN1eC3
C1eN2eN3
N2eN3eC11
C2eC1eC8
N2eC1e C2
N2eC1eC8
N1eC2eC1
N1eC3eC8
N1eC3eC4
C7eC8eC1
C7eC8eC3
C1eC8eC3
N3eC11eC12
N3eC11eC16
C12eC11eC16
Torsion
109.2 (2)
113.8 (2)
112.7 (2)
107.5 (2)
120.5 (2)
132.0 (2)
109.2 (2)
108.5 (2)
129.5 (3)
135.8 (2)
118.6 (2)
105.6 (2)
115.2 (3)
125.3 (3)
119.4 (3)
109.2
109.4(3)
113.5(3)
113.4(3)
108.2(3)
120.2(3)
131.5(3)
108.7(3)
108.4(3)
130.1(3)
135.8(3)
118.9(3)
105.3(3)
115.1(3)
125.8(3)
119.1(3)
109.2
109.1(4)
114.4(4)
112.4(4)
107.4(4)
120.3(5)
132.3(4)
109.1(4)
108.6(4)
129.5(5)
136.0(4)
118.3(5)
105.7(4)
115.9(4)
125.2(4)
118.8(4)
109.9(4)
113.6(4)
113.7(4)
107.6(4)
120.3(4)
132.0(4)
108.6(4)
108.0(4)
130.1(5)
135.3(4)
118.8(4)
105.9(4)
116.1(4)
125.0(4)
118.7(4)
109.2
115.8
115.1
107.5
120.4
132.1
109.0
108.4
129.1
135.1
118.9
105.9
116.1
125.3
118.6
109.8(4)
115.4(4)
114.8(3)
106.0(4)
121.4(4)
132.5(4)
109.1(4)
108.5(4)
127.9(4)
133.8(4)
119.3(4)
106.5(4)
114.3(5)
125.2(4)
120.3(4)
109.3
109.4(2)
114.6(2)
112.4(2)
107.3(2)
119.5(2)
133.2(3)
109.1(2)
108.1(2)
128.3(3)
135.9(3)
118.1(3)
106.0(2)
115.3(3)
125.4(3)
119.3(3)
109.4
115.9
114.9
107.5
120.3
132.1
108.9
108.4
129.1
135.1
118.9
105.97
115.6
125.0
119.4
115.9
114.9
107.5
120.4
132.1
109.0
108.4
129.1
135.1
118.9
105.9
115.9
125.3
118.8
116.0
114.7
107.5
120.3
132.2
109.0
108.4
129.1
135.1
119.0
105.9
115.8
125.1
119.1
116.0
114.5
107.5
120.3
132.3
108.9
108.4
129.0
135.1
119.1
105.8
115.7
125.1
119.2
C1eN2eN3eC11
N2eN3eC11eC12
N2eN3eC11eC16
N3eN2eC1eC2
N3eN2eC1eC8
ꢀ179.9(1)
166.1 (2)
ꢀ15.8 (4)
178.9 (2)
ꢀ1.8 (4)
180.0
180.0
0.0
180.0
0.0
176.6(2)
174.1(3)
ꢀ8.5 (5)
179.9(3)
ꢀ4.3 (5)
ꢀ179.8
ꢀ178.6
1.4
178.2(3)
ꢀ10.7(6)
170.9(3)
179.2(4)
ꢀ4.7(6)
175.1(3)
ꢀ16.2(6)
168.2(4)
ꢀ177.6(4)
ꢀ3.1(6)
ꢀ180.0
0.0
ꢀ179.9
ꢀ180.0
0.0
173.0(3)
174.9(3)
0.0
177.5(4)
ꢀ7.0(3)
180.0
180.0
0.0
180.0
0.0
179.1(2)
178.2(2)
ꢀ1.6(4)
178.0(2)
ꢀ1.1(4)
180.0
ꢀ180.0
0.0
ꢀ179.7
ꢀ180.0
0.3
0.0
a
Ref. [15].
On the other hand, the absorption maxima exhibit the little
bathochromic shifts for each dye by increasing the dielectric con-
stants. For dye 1, the biggest change is 7 nm in DMSO with respect
to the value in chloroform. Similar trends were seen for dyes 2 and
3 with the value of 5 nm and for dyes 4 and 5 with the value of
7 nm. According to these findings, no significant solvent effects on
the absorption maxima for dyes 1e5 were observed experimen-
tally. The results of theoretical calculations are in accordance with
these experimental results. Thus, it can be said that any change in
the molecular structures of these dyes is not observed on different
application environments. These obtained results are important for
using of dyes in application process in different media.
The effects of the substituents on the absorption maxima could
also be found from Table 4. The absorption maxima for dyes 2 and 3
including the electron-donating groups X ¼ CH3 and X ¼ OCH3 do
not show significant changes according to that of dye 1. On the
contrary, the absorption maxima move to longer wavelenghts for
dyes 4 and 5 including the electron-withdrawing groups X ¼ Cl and
X ¼ CN. A bathochromic shift results by increasing the intra-
molecular charge transfer from the indole ring to the azo unit with
the electron-withdrawing groups at para position of the phenyl
ring. However, this effect is more dominant for dye 5 than in dye 3
with the increase in the electron-withdrawing abilities of the
substituent in all solvents. The obtained results are compatible with
the experimental and theoretical data.
To further investigate the effects of the substituents and sol-
vents for dyes 1e5, the DFT calculations are carried out for the
highest occupied molecular orbital (HOMO) and the lowest unoc-
cupied molecular orbital (LUMO) gaps. In calculations, the ab-
sorption maxima of dyes 1e5 were found to correspond to the
electronic transitions from HOMO to LUMO. The obtained HOMO
and LUMO orbitals for all dyes in gas phase are shown in Fig. 5. As
can be seen in Fig. 5, for all dyes, each of the orbitals is delocalized
over the whole of the main skeleton of the dye. In Table 5, HOMO,
LUMO energies and energy gap (Egap) between the HOMO and
LUMO for dyes 1e5 for the solvents are given. The obtained results

B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
67
Fig. 3. a). A partial packing diagram for dye 2. (b). A view of the cyclic tetramer for dye 3 formed by CeH.O short contacts (shown as dashed lines). (c). A partial packing diagram
for dye 4. (d). A packing diagram for dye 5 viewed down the c-axis.
indicate that, the energies of HOMO and LUMO are increased for
dyes 2 and 3 as compared to dye 1. For dyes 2 and 3, the reason for
increase in the energies of HOMO and LUMO is that the electron
density on the whole system increases as a result of the electron-
donating groups eCH3 and eOCH3 at para position of the phenyl
ring. Contrary, the energies of HOMO and LUMO for dyes 4 and 5
decrease with respect to the corresponding values in dye 1, because
of the decrease in the electron density with the effects of the
electron-withdrawing groups. However, Egap values for each dye
decrease with the effects of both electron-donating and electron-
withdrawing groups. At the same time, the solvent effects are lit-
Table 3
ꢁ ꢁ
Parameters (A, ) for hydrogen bonds and short intramolecular contacts for dyes 2e5.
tle on the value of Egap. When the dielectric constant ( ) of the
3
XeH/Cg(
p
-ring)
H/Cg
X/Cg
<YeX/Cg
Symmetry codes
solvents increases, a small reducing in Egap is seen in all dyes.
2
C5eH5/Cg3
C10eH10A/Cg2
C10eH10B/Cg1
3
C17eH17F/Cg4
C17eH17A/O10
C120eH12’/O1
4
C5eH5/Cg3
C10eH10A/Cg1
C10eH10B/Cg2
5
C9eH9B/Cg3
C10eH10A/Cg2
2.90
2.66
2.75
3.587(4)
3.525(4)
3.488(4)
132
150
135
-x, ½þy, ½-z
-x,-y,1-z,
1-x,-y,1-z
3.4. Molecular electrostatic potential (MEP)
The molecular electrostatic potential (MEP) is derived from the
electronic density. MEP is a helpful tool to understand the sites of
the electrophilic attack and the nucleophilic reactions as well as
hydrogen-bonding interactions [35e37]. MEP at the B3LYP/6-
311þG(d,p) optimized geometry was calculated to predict the
reactive sites for the electrophilic and nucleophilic attacks in dyes
1e5. The negative (red) and the positive (blue) regions of the MEP
were related to the electrophilic and nucleophilic reactivities,
respectively, as shown in Fig. 6. As can be seen in Fig. 6, the
2.86
2.55
2.71
3.616(6)
3.460(7)
3.353(6)
137
158
127
1-x,-y,-z
2-x,2-y,2-z
x-1,þy,þz
2.91
2.58
2.78
3.598(6)
3.460(7)
3.523(7)
131
153
135
1-x,-1/2 þ y,1/2-z
-x,1-y,-z
1-x,1-y,-z
2.64
2.82
3.516(3)
3.627(4)
152
143
-x,1-y,1-z
1-x, 1-y,1-z.
Cg(
p
-ring).Cg(
p
-ring)
Cg.Cg
Symmetry codes
2
Table 4
Cg1 . Cg1
Cg3 . Cg3
3
3.627(2)
3.852(2)
ex, e y, 1 e z
1ex, ey, e z
Calculated and experimental absorption wavelengths (lmax) for dyes 1e5 in different
solvents. The oscillator strengths (f) are given in parentheses.
Cg1 . Cg5iii
4
3.732(2)
xe1, y, z
Dye
DMSO
Exp.
A. Acid
Exp.
Chloroform
Calc.
Calc.
Exp.
Calc.
Cg1 . Cg1
Cg3 . Cg3
5
3.665(6)
3.816(6)
-x,1-y,-z
-x,1-y,1-z
1
2
3
4
5
387
387
389
393
414
390 (0.94)
393 (1.01)
399 (1.07)
398 (1.03)
420 (1.14)
385,437
385,448
384,466
387
387 (0.92)
389 (1.00)
396 (1.05)
395 (1.02)
416 (1.11)
380
382
384
386
406
388 (0.94)
390 (1.01)
397 (1.07)
396 (1.03)
418 (1.13)
Cg1 . Cg1
3.626(6)
-x,1-y,-z
Cg1, Cg2, Cg3 and Cg4 are the centroids of the rings (N1/C1eC3/C8), (C3eC8), (C11e
C16) and (C110eC160), respectively.
407

68
B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
X
X
X
N
N
N
N
CH3COOH
N
N
H
H
CH3
CH3
CH3
N
CH3
N
CH3
N
CH3
1.X=H
2.X=CH3
3.X=OCH3
Fig. 4. Protonated azo form and its resonance stabilized iminium-hydrazone structure.
negative regions are mainly localized on the diazo groups in the
dyes. Additionally, the negative potential sites are the oxygen
atom in dye 3 and the nitrogen atom of the cyano group in dye 5.
The positive potential sites are the hydrogen atoms of methyl
groups on indole ring and around the hydrogen atoms of the
methoxy groups in dye 3.
3.5. Dipol moments
Table 5 also shows a comparison of the dipole moments of dyes
1e5 in different solvents. While the dipole moments of dyes 2 and 3
decrease with the electron-donating groups, the dipole moments of
dyes 4 and 5 increase with the electron-withdrawing groups with
Fig. 5. Computed orbitals for dyes (1e5).

B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
69
Table 5
HOMO-LUMO orbital energies, Egap and dipole moment values for dye 1e5 in different solvents.
Dye
m
(Debye)
HOMO (eV)
LUMO (eV)
Egap (eV)
m
(Debye)
HOMO (eV)
LUMO (eV)
Egap (eV)
m
(Debye)
HOMO (eV)
LUMO (eV)
Egap (eV)
DMSO
Acetic acid
Chloroform
1
2
3
4
5
6.53
5.76
3.87
8.78
13.80
ꢀ5.73
ꢀ5.65
ꢀ5.52
ꢀ5.75
ꢀ5.89
ꢀ2.23
ꢀ2.17
ꢀ2.09
ꢀ2.32
ꢀ2.66
3.50
3.48
3.43
3.43
3.23
5.960
5.247
3.452
8.143
12.952
ꢀ5.67
ꢀ5.59
ꢀ5.46
ꢀ5.71
ꢀ5.88
ꢀ2.16
ꢀ2.09
ꢀ2.01
ꢀ2.27
ꢀ2.62
3.51
3.50
3.45
3.44
3.26
5.782
5.086
3.325
7.941
12.673
ꢀ5.65
ꢀ5.57
ꢀ5.45
ꢀ5.70
ꢀ5.88
ꢀ2.13
ꢀ2.06
ꢀ1.98
ꢀ2.25
ꢀ2.61
3.52
3.51
3.47
3.45
3.27
respect to that of dye 1 in each solvent. Similarly, the solvent effects
on the dipole moments of dyes 1e5 are not pronounced.
compared with the theoretical calculations. Generally, the obtained
experimental data are compared with the theoretical calculations
and the results are compatible but all of the computed N2]N3
bonds are slightly shorter than the experimental ones. The mo-
lecular structures of the dyes are stable in different solvent media.
The dyes have strong single absorption bands in all solvents except
4. Conclusions
In summary, a new series of phenylazoindole based dyes were
synthesized and fully characterized. The molecular structures of the
dyes were characterized by using X-ray structural analyses and
of acetic acid. In acetic acid, the dyes (1e3) were protonated via b-
nitrogen atom of the azo group.
Fig. 6. MEP map calculated at B3LYP/6-311þ(d,p) level for (a) dye 1, (b) dye 2, (c) dye 3, (d) dye 4, (e) dye 5.

70
B. Babür et al. / Dyes and Pigments 103 (2014) 62e70
ꢀ
ꢀ
[16] Seferoglu Z, Yalçın E, Babür B, Seferoglu N, Hökelek T, Yılmaz E, et al. Phe-
nylazoindole dyes-Part I: the syntheses, characterizations, crystal structures,
quantum chemical calculations and antimicrobial properties. Spectrochim
Acta A 2013;113:314e24.
Acknowledgments
The theoretical part of this work is supported by a grant from
Gazi University (BAP: 18/2011-06).
[17] Lee CT, Yang WT, Parr RG. Development of the Colle-Salvetti correlation-en-
ergy formula into a functional of the electron density. Phys Rev B 1988;37:
785e9.
[18] Becke AD. Density-functional thermochemistry. III. The role of exact ex-
change. J Chem Phys 1993;98(7):5648e52.
Appendix A. Supplementary material
[19] Hariharan PC, Pople JA. The influence of polarization functions on molecular
orbital hydrogenation energies. Theor Chem Acc 1973;28:213e22.
[20] Tomasi J, Cammi R, Mennucci B, Cappelli C, Corni S. Molecular properties in
solution described with a continuum solvation model. Phys Chem Chem Phys
2002;24:5697e703.
[21] Cossi M, Barone V. Time-dependent density functional theory for molecules in
liquid solutions. J Chem Phys 2001;115:4708e17.
[22] Bauernschmitt R, Ahlrichs R. Treatment of electronic excitations within the
adiabatic approximation of time dependent density functional theory. Chem
Phys Lett 1996;256:454e64.
CCDC-924115, 924116, 937360 and 924117 contain the supple-
mentary crystallographic data for the structures 2e5 respectively.
These data can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: þ44 1223 336033; e-mail: deposit@
ccdc.cam.ac.uk).
References
[23] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, et al.
Gaussian 09, revision A.2. Wallingford CT: Gaussian, Inc.; 2009.
[24] Rigaku/MSC, Inc., 9009 new Trails Drive, The Woodlands, TX 77381.
[1] Hunger K. Industrial dyes chemistry, properties and applications. Weinheim:
Wiley-VCH Verlag; 2003. pp. 14e35.
[25] Sheldrick GM.
A short history of SHELX. Acta Crystallogr 2008;A 64(1):
[2] Catino SC, Farris RE. Azo dyes. In: Grayson M, editor. Concise encyclopedia of
chemical techonogy. New York: John Wiley and Sons; 1985. pp. 142e4.
[3] Zollinger H. Color chemistry: synthesis, properties and applications of organic
dyes and pigments. 3rd ed. Switzerland: Wiley-VCH; 2003. p. 183.
[4] Tong X, Zhao Y. Multiple photochemical processes in liquid crystalline azo
dye-doped liquid crystals. Chem Mater 2009;21(17):4047e54.
[5] Tanaka K, Matsuo K, Nakanishi A, Misako J, Shiota H, Yamaguchi M, et al.
Syntheses and antimicrobial activities of five-membered heterocycles having
a phenylazo substituent. Chem Pharm Bull 1984;32(8):3291e8.
[6] Fadda AA, Etmen HA, Amer FA, Barghout M, Mohammed KS. Azo disperse dyes
for synthetic fibres. I: 2-Methyl- and 2-phenylquinazolone derivatives. J Chem
Technol Biotechnol 1994;61(4):343e9.
112e22.
[26] Dawson JF. The structure and properties of disperse dyes in polyester color-
ation. J Soc Dyers Col 1983;99(7e8):183e91.
[27] Annen O, Egli R, Hasler B, Jakob H, Matzinger P. Replacement of disperse
anthraquinonedyes. Review Progress Coloration Related Topics1987;17:72e85.
[28] Leadbetter PW, Leaver AT. Disperse dyes e the challenge of the 1990s. Meeting
demands for increasingly higher levels of washfastness in the exhaust dyeing
of polyester/cellulosic blends. Review Progress Coloration Related Topics
1989;19:33e9.
ꢀ
[29] Seferoglu Z, Hökelek T, S¸ ahin E, Ertan N. 3-(4-Chlorophenyldiazenyl)-1-
methyl-2-phenyl-1H-indole. Acta Crystallogr 2006;E 62:o2108e10.
ꢀ
[30] Seferoglu Z, Hökelek T, S¸ ahin E, Ertan N. N-{4-[(2-Phenyl-1H-indol-3-yl)dia-
[7] Isaad J, Perwuelz A. New color chemosensors for cyanide based on water
soluble azo dyes. Tetrahedron Lett 2010;51:5810e4.
zenyl]phenyl}acetamide. Acta Crystallogr 2006;E 62:o3492e4.
ꢀ
[31] Seferoglu Z, Hökelek T, S¸ ahin E, Ertan N. Ethyl [2-(2-phenyl-1H-indol-3-
[8] Wang Q, Long Y, Liangliang L, Chuanzheng Z, Zhen X. A thermostable azo-
linker for reversible photoregulation of DNA replication. Tetrahedron Lett
2008;49:5087e9.
yldiazenyl)-1,3-thiazol-4-yl]acetate. Acta Crystallogr 2006;E 62:o3835e7.
[32] Aktan E, Babür B, Seferoglu Z, Hökelek T, S¸ ahin E. Synthesis and structure of a
novel hetarylazoindole dye studied by X-ray diffraction, FT-IR, FT-Raman, UV-
vis, NMR spectra and DFT calculations. J Mol Struct 2011;1002:113e20.
[33] Aktan E, Seferoglu Z, Hökelek T, S¸ ahin E. The synthesis, characterisation and
ꢀ
[9] Wang J, Ha CS. A colorimetric and fluorescent turn-on chemosensor for Zn2þ
based on an azobenzene-containing compound. Tetrahedron 2009;65:6959e64.
[10] DiCesare N, Lakowicz JR. New color chemosensors for monosaccharides based
on azo dyes. Org Lett 2001;3(24):3891e3.
ꢀ
molecular structure of a new hetarylazoindole dye studied by X-ray diffrac-
tion, spectral analysis and density functional theory calculation. Color Technol
2012;128:371e7.
[11] Ingram A, Stokes RJ, Redden J, Gibson K, Moore B, Faulds K, et al. 8-
Hydroxyquinolinyl azo dyes: a class of surface-enhanced resonance Raman
scattering-based probes for ultrasensitive monitoring of enzymatic activity.
Anal Chem 2007;79(22):8578e83.
[12] Coelho PJ, Cidália M, Castro R, Maurício A, Fonseca C, Manuela M, et al. Pho-
toswitching in azo dyes bearing thienylpyrrole and benzothiazole heterocyclic
systems. Dyes Pigm 2012;92(1):745e8.
[34] Kelemen J, Kormany G, Rihs G. Azo-hydrazone tautomerism in azo dyes. III.
The tautomeric structure of 1-(40-nitrophenylazo)-2-naphthylamine from
crystal structure determination. Dyes Pigm 1982;3:249e71.
[35] Scrocco E, Tomasi. Electronic molecular structure, reactivity and intermolec-
ular forces: an Euristic interpretation by means of electrostatic molecular
potentials. J Adv Quantum Chem 1978;11:115e21.
[13] Kim YD, Cho JH, Park CR, Choi JH, Yoon C, Kim JP. Synthesis, application and
investigation of structureethermal stability relationships of thermally stable
water-soluble azo naphthalene dyes for LCD red color filters. Dyes Pigm
2011;89(1):1e8.
[14] Schueren LV, Hemelsoet K, Speybroeck VV, Clerck KD. The influence of a
polyamide matrix on the halochromic behaviour of the pH-sensitive azo dye
nitrazine Yellow. Dyes Pigm 2012;94(3):443e51.
[36] Luque FJ, Lopez JM, Orozco M. Perspective on “Electrostatic interactions of a
solute with a continuum. A direct utilization of ab initio molecular potentials
for the prevision of solvent effects”. Theor Chem Acc 2000;103(3e4):343e5.
[37] Okulik N, Jubert AH. Theoretical analysis of the reactive sites of non-steroidal
anti-inflammatory drugs. Int Electron J Mol Des 2005;4:17e30.
[38] Farrugia LJ. ORTEP-3 for Windows e a version of ORTEP-III with a graphical
user interface (GUI). J Appl Cryst 1997;30:565.
[15] Hökelek T, Biçer NT, Seferoglu Z, Sahin E. 3-Phenyldiazenyl-1,2-dimethyl-1H-
indole. Acta Crystallogr 2010;E66:o2311.