Phenylazoindole dyes - Part I: The syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties

Article abstract of DOI:10.1016/j.saa.2013.04.081

(Chemical Equation Presented) In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characteri

Full text of DOI:10.1016/j.saa.2013.04.081

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Phenylazoindole dyes – Part I: The syntheses, characterizations, crystal
structures, quantum chemical calculations and antimicrobial properties
a
a
b
Zeynel Seferog˘lu a, , Ergin Yalçın , Banu Babür , Nurgül Seferog˘lu ,
⇑
Tuncer Hökelek c, Ebru Yılmaz d, Ertan Sßahin e
a Gazi University, Department of Chemistry, 06500 Ankara, Turkey
b Gazi University, Advanced Technologies, 06500 Ankara, Turkey
c Hacettepe University, Department of Physics, 06800 Ankara, Turkey
d Gazi University, Vocational School of Health Sciences, 06830 Ankara, Turkey
e Atatürk University, Department of Chemistry, Erzurum, Turkey
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Phenylazoindole based new organic
dyes have been synthesized and
characterized.
ꢀ
The most stable tautomeric form of
the dyes have been determined easily
with using model compounds in
solution.
ꢀ
The quantum chemical calculations
results showed that the azo tautomer
is dominant tautomeric form.
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, the synthesis of four new phenylazo indole dyes (dye 1–4) were carried out by diazotization
of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes
were characterized by UV–vis, FT-IR, 1H NMR, HRMS and X-ray single crystal diffraction methods. Azo–
hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chlo-
roform) was investigated by using 1H NMR and UV–vis results. The experimental results were compared
with the corresponding calculated values. The results of experimental data and theoretical calculations
showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicro-
bial activity of the dyes was also evaluated.
Received 10 October 2012
Received in revised form 1 March 2013
Accepted 24 April 2013
Available online 14 May 2013
Keywords:
Phenylazoindole dye
Azo–hydrazone tautomer
Crystal structure
Published by Elsevier B.V.
DFT calculations
Antimicrobial activity
Introduction
fundamental and application [1]. It has been known for many years
that the azo compounds are the most widely used class of dyes,
Azo compounds, with two phenyl or hetaryl rings separated by
an azo (N@N) bond, are versatile molecules and have been used as
due to their versatile applications in various fields such as the dye-
ing of textile fibers, the coloring of different materials, colored
plastics and polymers, biological–medicinal studies, as chemosen-
sor and advanced applications in organic synthesis [2–9]. They are
also used in the fields of nonlinear optics and optical data storage
[10–12]. Their optical properties depend on not only the
dyes and pigments for
a long time in research areas both
⇑
Corresponding author. Tel.: +90 312 2021525; fax: +90 312 2122279.
E-mail address: znseferoglu@gazi.edu.tr (Z. Seferog˘lu).
1386-1425/$ - see front matter Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2013.04.081

Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
315
spectroscopic properties of the molecules, but also their crystallo-
graphic arrangements [13,14]. Carbocyclic diazo components have
been used extensively in the preparation of disperse dyes. These
dyes are also characterized by having generally excellent bright-
ness and high extinction coefficients and also many carbocyclic
diazo components have been current potential dyestuffs in dye
industry. On the other hand, many azo dye breakdown products
are carcinogenic, toxic and mutagenic for life [15]. However, the
antimicrobial activity of some azo dyes has been reported previ-
ously [16–19].
Tautomerism is quite interesting from a theoretical viewpoint
and it is also important from a practical standpoint because the
two tautomers have different technical properties [20]. Azo–hydra-
zone, annular tautomerism and other tautomeric structures that
exist in the azo compounds have been extensively attempted by
several researchers to recognize their exact geometrical structures
and stability in gas phase (theoretically) and in the presence of sol-
vent molecules. The azo/hydrazone tautomerism of hydroxy and
amino substituted azo compounds has been intensively studied
but enamine type azo compounds have not been investigated dee-
ply. Therefore, tautomeric equilibria of phenylazo dyes prepared
from enamine-type coupling components need to be considered.
The aim of this study is to determine the most stable tautomeric
form of some new phenylazoindole dyes in solution and solid state.
For this purpose, four compounds (dyes 1–4) were synthesized for
the first time and characterized by using the spectroscopic tech-
niques (UV–vis, FT-IR, 1H NMR, HRMS). The crystalline and molec-
ular structures of dyes 2 and 4 obtained by X-ray diffraction
analysis were evaluated. In addition, the geometry optimizations,
the stabilities and maximum absorption wavelengths of the dyes
in gas phase and in solution state and 1H NMR chemical shifts of
the dyes 1–4 were discussed. Also, antimicrobial activities of the
dyes were investigated.
coli, Klebsiella pneumoniae, Enterobacter sakazakii liquid cultures
were prepared in brain heart infusion broth for their antimicrobial
activity tests and Candida albicans, Candida tropicalis were prepared
in Sabouraud dextrose broth for its antifungal activity tests. The
dyes were dissolved in DMSO at concentrations of 10 mg mLꢁ1
using a Millipore membrane filter (0.45 mL, Millipore, USA). Anti-
microbial activity of DMSO against the test organisms was also
investigated, but was found to have no antimicrobial activity
against any of the organisms. Approximately 1 cm3 of a 24 h broth
culture containing 106 cfu cmꢁ3 was placed in sterile Petri dishes.
Moltent nutrient agar (15 cm3) kept at 45 °C was then poured into
the Petri dishes and allowed to solidify. Six milimeter diameter
holes were then punched carefully using a sterile cork borer and
completely filled with the test solutions. The plates were incubated
for 24 h at 37 °C. After 24 h., the inhibition zone that appeared
around the holes in each plate was measured. Sulbactam ampicillin
(SAM), Gentamisin (CN), Sulfamethoxazole Trimethoprim (SXT)
and Miconazole (MCZ) were screened under similar conditions as
a reference Standard.
In this work, 2 Staphylococus aureus, 2 S. saprophyticus, 1 Listeria
monocytogenes, 1 L. innocua (Gram Positive), 4 Pseudomonas aeru-
ginosa, 2 P. putida, 5 Escherichia coli, 2 Klebsiella pneumoniae, 2
Enterobacter sakazakii (Gram Negative), 2 Candida albicans, 1 Can-
dida tropicalis (Yeast) were used to investigate the antibacteriolog-
ical and antifungal activities of synthesized dyes 1–4. Used
microorganisms were isolated from Gazi University, Faculty of Sci-
ence and Arts, Department of Biology.
Preparation of dyes (1–4)
Various carbocyclic amines can be diazotized with HCl and
NaNO2. A typical procedure of diazotizing and coupling is that de-
scribed below used for 4-aminoacetophenone and 2-methylindole;
all other compounds were prepared in a similar manner. The yields
of the dyes are in the range of 78–90%. The obtained compounds
were purified by crystallization using ethanol and then analyzed.
Experimental
Material and methods
Preparation of (E)-1-(4-((2-methyl-1H-indol-3-
yl)diazenyl)phenyl)ethanone (1)
The chemicals used in the synthesis 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
4-Aminoacetophenone (0.27 g, 2 mmol) was dissolved in con-
centrated HCl (1.5 mL, 36 % (w/w)) and water (4 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 diazo-
in KBr (m
are in cmꢁ1). H NMR spectra were recorded on a Bruker-
Spectrospin Avance DPX 400 Ultra-Shield in DMSO-d6. Chemical
shifts are expressed in d units (ppm). Ultraviolet–visible (UV–vis)
absorption spectra were recorded on Analytik Jena Specord 200
spectrophotometer at the wavelength of maximum absorption
(kmax, in nm) in the solvents specified. The methanolic solutions
of the dyes were examined, when was added 0.1 mL KOH (0.1 M)
or 0.1 mL HCl to 1 mL of the dye solutions. Mass spectra were re-
corded on 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.
nium salt was cooled in
a salt/ice mixture. 2-Methylindole
(0.26 g, 2.0 mmol) was dissolved in a mixture of acetic acid and
propionic acid solution (3:1, 8 mL) and cooled in an ice bath. Then,
cold diazonium solution was added to this cooled solution by stir-
ring in a dropwise manner. The solution was stirred at 273–278 K
for 1 h. The pH of the reaction mixture was maintained at 4–6 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 dried.
Recrystallization from ethanol gave orange crystals (MW: 277
Microorganisms
g/mol, yield: 0.25 g, 90%; m.p.: 246 °C) FT-IR (KBr)
(NH indole), 3067 (aromatic CAH), 2910 (aliphatic CAH), 1661
(C@O), 1593 (C@C) cmꢁ1 1H NMR (DMSO-d6): d 12.20 (brs, NH
mmax: 3236
The antimicrobial activities of the synthesized dyes (1–4) were
determined by the well-diffusion method [21]. 2 Staphylococus aur-
eus, 2 S. saprophyticus, 1 Listeria monocytogenes, 1 L. innocua (Gram
Positive), 4 Pseudomonas aeruginosa, 2 P. putida, 5 Escherichia coli, 2
Klebsiella pneumoniae, 2 Enterobacter sakazakii (Gram Negative),
and 2 Candida albicans, 1 Candida tropicalis (fungus) were used to
investigate the antibacterial and antifungal activities of synthe-
sized dyes. Staphylococus aureus, S. saprophyticus, Listeria monocyt-
ogenes, L. innocua, Pseudomonas aeruginosa, P. putida, Escherichia
;
indole), 8.39 (d, 1H), 8.11 (d, 2H), 7.90 (d, 2H), 7.41 (d, 1H), 7.20
(m, 2H), 2.80 (s, 3H), 2.68 (s, 3H). HRMS (m/z): (M+H)+ calcd for
C17H15N3O 278.1293; found, 278.1293.
(E)-1-(4-((1,2-dimethyl-1H-indol-3-yl)diazenyl)phenyl)ethanone (2)
The dye was obtained from 4-aminoacetophenone and 1,2-
dimethylindole as orange crystals (MW: 291 g/mol, C18H17N3O
yield: 0.26 g, 88%; m.p.: 136 °C)
mmax: 3050 (aromatic CAH),

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2910, 2870 (aliphatic CAH), 1672 (C@O), 1600, 1530 (C@C) cmꢁ1
;
The electronic spectra of the compounds in azo form were also
obtained in the framework of TD-DFT calculations with B3LYP
using 6-311g(d,p) basis set. In these calculations, different solvents
was used to evaluate of the solvent effects on maximum absorp-
tion wavelength for each molecule.
1H NMR (DMSO-d6): d 8.43 (d, 1H), 8.10 (d, 2H), 7.90 (d, 2H), 7.58
(d, 1H), 7.30 (m, 2H), 3.81 (s, 3H, ANCH3), 2.80 (s, 3H), 2.61 (s, 3H).
HRMS (m/z): (M+H)+ calcd for C17H15N3O 292.1450; found,
292.1446.
Crystallography
(E)-1-(4-((2-phenyl-1H-indol-3-yl)diazenyl)phenyl)ethanone (3)
The dye was obtained from 4-aminoacetophenone and 2-phen-
ylindole as orange crystals (MW: 339 g/mol, yield: 0.28 g, 83%;
The X-ray diffraction data collections were performed on a Rig-
m.p.: 227 °C)
m
max: 3263 (NH indole), 3063 (aromatic CAH), 2928
aku R-AXIS RAPID-S diffractometer using Mo Ka radiation
(aliphatic CAH), 1656 (C@O), 1594 (C@C) cmꢁ1
;
1H NMR (DMSO-
(k = 0.71073 Å) at T = 298 K. Absorption corrections by multi-scan
[26] were applied. The structures were analyzed using a combina-
tion of direct and difference Fourier methods provided by the
SHELXS97 [27] and were refined as full-matrix least squares
against F2 using all data by the SHELXL97 [27] computer programs;
all non-hydrogen atoms were refined anisotropically. H atoms
were positioned geometrically at distances of 0.93 (CH) and
0.96 Å (CH3) from the parent C atoms; a riding model was used
during the refinement processes and the Uiso(H) values were con-
strained to be xUeq(carrier atom), where x = 1.5 for methyl H, and
x = 1.2 for aromatic H atoms. Crystal data and details of the struc-
ture determinations for dyes 2 and 4 are summarized in Table 1.
d6): d 12.52 (brs, NH indole), 8.51 (d, 1H), 8.21 (d, 2H), 8.12 (d,
2H), 7.90 (d, 2H), 7.64 (m, 2H), 7.51 (m, 2H), 7.30 (m, 2H), 2.65
(s, 3H). HRMS (m/z): (M+H)+ calcd for C22H17N3O 340.1442; found,
340.1438.
(E)-1-(4-((1-methyl-2-phenyl-1H-indol-3-
yl)diazenyl)phenyl)ethanone (4)
The dye was obtained from 4-aminoacetophenone and 1-
methyl-2-phenylindole as red crystals (MW: 353 g/mol, yield:
0.27 g, 77%; m.p.: 279 °C)
m
max: 3028 (aromatic CAH), 2924 (ali-
phatic CAH), 1674 (C@O), 1593 (C@C) cmꢁ1
;
1H NMR (DMSO-d6):
d 8.52 (d, 1H), 8.08 (d, 2H), 7.72–7.80 (m, 6H), 7.60 (d, 2H), 7.40
(m, 2H), 3.88 (s, 3H, ANCH3), 2.62 (s, 3H). HRMS (m/z): (M+H)+
calcd for C23H19N3O 354.1606; found, 354.1600.
Results and discussion
The phenylazoindole dyes (1–4) were prepared by coupling 2-
methylindole, 1,2-dimethylindole, 2-phenylindole and 1-methyl-
2-phenyl indole with diazotized 4-aminoacetophenon in dilute
hydrochloric acid (Scheme 1). The dyes (1–4) were obtained gener-
ally in excellent yields (90–77%); the structure of these dyes were
verified by spectroscopic methods (FT-IR, Mass and 1H NMR). Phys-
ical and spectral data of dyes prepared are given in experimental
section. The dyes prepared from 2-methylindole (dye 1) and 2-
phenylindole (dye 3) may exist in two possible tautomeric forms,
namely azo form A and hydrazone form B, as depicted in Scheme 2.
The protonation and deprotonation of the two tautomers lead to
the common anion C and cation D.
The infrared spectra of dyes 1 and 3 (in KBr) showed weak and
broad band in the 3236 and 3263 cmꢁ1, due to the ANH band of
the indole rings. 1H NMR spectra of the dyes showed the ANH
peaks in the range of 12.52–12.20 ppm in DMSO-d6. These results
suggest that the dyes 1 and 3 are predominantly exist in the azo
form in the solid state and into solution (DMSO).
Computational study
All calculations were performed with the aid of the GAUSSIAN
09 software [22]. Becke’s three-parameter exact-exchange func-
tional (B3), combined with the gradient-corrected correlation func-
tional of Lee–Yang–Parr (LYP) of the density functional theory
methods (B3LYP) [23] were used for geometry optimizations. 6-
311+g(d,p) Basis set was used in all optimization calculations.
The optimized structures were characterized as true minima by
vibrational frequency calculations. The optimized structure in gas
phase was used for NMR calculations. The calculations of
1H NMR chemical shielding in DMSO for all dyes were performed
using GIAO/DFT [24,25] method at 6-311+g(d,p) basis sets.
The 1H-shieldings were converted into the predicted chemical
shifts using dTMS values for shielding constant of tetramethylsilane
hydrogens calculated at the same level of theory according to the
general expression dCal = dTMS ꢁ d.
Table 1
Crystal data and details of the structure determinations for dyes 2 and 4.
Empirical formula
Formula weight
Crystal dimensions (mm)
Temperature (K)
Crystal system
Space group
a (Å)
C18H17N3O (2)
291.35
C23H19N3O (4)
353.41
0.20 ꢂ 0.20 ꢂ 0.10
0.35 ꢂ 0.25 ꢂ 0.20
294
294
Monoclinic
P21/n
Monoclinic
P21/c
9.8216(4)
11.7784(3)
13.5508(4)
100.692(2)
1540.38(9)
4
1.256
52.8
0.08
10.2842(2)
17.5313(3)
21.1442(5)
101.282(3)
3738.53(14)
8
1.256
56.0
0.08
b (Å)
c (Å)
b (°)
Volume (Å3)
Z
Dcalc (g cmꢁ3
2hmax (°)
)
l
(mmꢁ1
)
No. of reflections measured
No. of reflections observed [I > 2
No. of variables
31,380
2296
3142
102,670
4273
11,432
D
(I)]
R/Rw values
Color/shape
0.0698/0.1311
Orange/plate
0.000
0.400 and ꢁ0.290
0.073/0.223
Red/block
0.000
0.150 and ꢁ0.250
Maximum shift in final cycles
Largest diffraction peak and hole (e Åꢁ3
)

Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
317
4
4
5
20
16
5
15
11
19
17
14
12
3
2
3
2
O
O
18
13
6
N
N
6
21
1
15
16
1
10
N
CH3
7
N
CH3
17
7
22
N
8
N
8
14
R
R
9
CH3
9
13
10
11
12
R= H (dye 1); R= CH3 (dye 2)
R= H (dye 3); R= CH3 (dye 4)
(a)
(b)
Scheme 1. Structures of dyes.
Solvent effects on absorption spectra of the dyes
The absorption curves of dyes 1–4 in various solvents are shown
in Fig. 1. When kmax values of dye 1 are compared with its corre-
sponding model compound (dye 2), dye 1 is in favor of the predom-
inantly azo form in all solvents used (Fig. 1a and b). The small
hypsochromic and bathochromic shifts in kmax of these dyes in
used solvents are due to solute–solvent interactions. Dye 1 showed
absorption maxima at 409 nm in acetic acid, 409 nm in DMSO,
402 nm in methanol, 397 nm in chloroform (Table 2). The similar
The azo dyes are the most important commercial coloring
materials. Thus, determination of the dominant tautomeric struc-
ture of azo dyes in different solutions which has different poten-
tial tautomeric structures, is quite important. In this work, the
absorption spectra of phenylazoindole dyes (1–4) were recorded
over the range of k between 300 and 700 nm using a variety of
solvents in concentrations 10ꢁ6–10ꢁ8 M. In order to understand
the most stable tautomeric form of the prepared dyes in solution,
the compounds (dyes 2 and 4) has been used as model com-
pound for dyes 1 and 3. The used solvents have different dielec-
absorption maximum values were observed for dye
2 (e.g.
414 nm in acetic acid, 413 nm in DMSO, 406 nm in methanol,
and 408 nm in chloroform). The same trend has been seen in the
dyes 3 and 4 (Fig. 1c and d, Table 2).
tric constants (
acid ( , 6.17) and chloroform (
Table 2.
The absorption maxima of the dyes were found to be indepen-
dent of the solution phase and did not have a correlation with the
dielectric constants of the solvents. The model compounds (2 and
4) exist in the solely azo form and their absorption maxima in dif-
ferent solvents were found to exhibit little solvent dependence.
e
), i.e. DMSO (
e
, 46.45), methanol (
e
, 32.66), acetic
The synthesized phenylazoindole dyes theoretically may be in-
volved in azo–hydrazone tautomers (Scheme 2). Thus, the role of
the azo–hydrazone tautomerism in relation to the visible absorp-
tion spectra and solvatochromic behavior of the dyes have also
been investigated. The visible absorption spectra of the prepared
dyes showed one absorption maximum in all solvents used, with
the exception of dye 3 in DMSO (Fig. 1c). Two absorption maxima
may indicate the presence of an azo–hydrazone tautomeric
e
e
, 4.81). The results are given in
H
N
O
O
N
N
CH3
N
CH3
N
N
H
CH3
CH3
(Azo-enamine)
(Hydrazone-imine)
a
b
H
H
O
O
N
N
N
CH3
N
CH3
N
N
CH3
CH3
(Anion)
(Cation)
c
d
Scheme 2. Tautomeric forms of dye 1.

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Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
Table 2
Absorption maxima of the dyes in solvent and acidic/basic solution.
kmax (nm)
DMSO
409
413
430,530
417
DMSO + piperidine
Methanol
Methanol + KOH
Methanol + HCl
A.Acid
Chloroform
Chloroform + piperidine
Dye 1
Dye 2
Dye 3
Dye 4
409,515
412
402
408
422
402
401
406
421
401
440
440
445
440
409
414
421
414
397
408
417
413
402
408
419
412
534
417
equilibrium or equilibrium between one of the tautomeric forms
and an anionic form.
4 nm in methanol, 0 nm in acetic acid and 5 nm in chloroform rel-
ative to kmax of 4 in the same solvents.
The visible absorption spectra of the dyes prepared indicated
that 1-methyl-2-phenyl substituted dyes (3 and 4) generally ab-
sorp bathochromically compared with the 1,2-dimethyl substi-
tuted dyes (1 and 2) in all solvents used (Table 2). The kmax
values of dye 1 showed bathochromic shifts in all solvents when
The effects of acid or base on the absorption maxima of the dyes
in solution were investigated and the results were shown in Ta-
ble 2. The absorption maximum of dye 1 in DMSO was quite sen-
sitive to the addition of piperidine, with the exceptions of the
model compounds (2 and 4) (Fig. 2a). kmax of dyes 1 and 3 showed
large bathochromic shifts when a small amount of piperidine was
compared with dye 3 (for dye 1,
20 nm in methanol, 12 nm in acetic acid and 20 nm in chloroform
relative to kmax of 3 in the same solvents). Presumably, the reso-
nance effect enhanced by an -electron-rich phenyl group is more
favored than the slightly strong field effect of a methyl group. The
similar increasing values of kmax results did not observe for the
model compounds. For dye 2, kmax values are 4 nm in DMSO,
Dkmax values are 21 nm in DMSO,
added to each of the solutions in DMSO. For dye 1,
Dkmax is 25 nm
D
in DMSO + piperidine relative to DMSO. Dye 3 has two absorption
maxima in DMSO (Fig. 2b). When a small amount of piperidine was
added, the absorption band of this dye significantly changed and
showed one dominant absorption maxima in long wavelength. It
indicated that dye 3 exists in only anionic form (C) in basic DMSO
p
D
D
Fig. 1. Absorption spectra in various solvents for (a) dye 1, (b) dye 2, (c) dye 3, (d) dye 4.

Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
319
Fig. 2. Absorption spectra of (a) dye 1 in basic DMSO and DMSO solution, (b) dye 3 in basic DMSO and DMSO solution, (c) dye 1 in acidic and basic solution.
and between the tautomeric forms and anionic forms in neutral
DMSO.
Crystal structure analyses
There was no significantly change in the spectra of the dyes
when 0.1 M KOH was added to the methanolic solutions of the
dyes. However, when a small amount of 0.1 M HCl was added to
the methanolic solutions of the dyes the kmax values showed large
bathochromic shifts and also only one absorption maximum was
observed. This indicates that the dyes exist in the cationic form
(D) in acidic methanolic solution (Fig. 2c). Spectral data for the var-
iously substituted azo dyes show that there was a general ten-
dency for the visible absorption band to more bathochromically
in accordance with the electron acceptor–donor chromogens in
the coupling and diazo component [28]. These compounds involve
a migration of electron density from the donor group towards the
azo group and the absorption maxima of this type of compounds
were shifted longer wavelength due to stabilization of excited state
has been increased. The prepared dyes that are converted cationic
form via carbonyl oxygen increased electron accepting properties
(Scheme 2). So, delocalization of electrons is also increased from
indole to diazenyl bridge and kmax values shift to the bathochromic
Several times, we try to obtained suitable single crystal to deter-
mine tautomeric structures of especially dyes 1 and 3 but it can be
onlyobtained for two molecules(dyes 2 and 4). While there was only
one molecule in the asymmetric unit for dye 2 (Fig. 3), the asymmet-
ric unit of dye 4, containing two crystallographically independent
molecules, in which geometries and conformations of them are
slightly different (Fig. 4). The selected bond lengths and angles for
dyes 2 and 4 are given in Table 3. An examination of the deviations
from the least-square planes through the individual rings showed
thatall of therings are planarin dyes 2 and 4. Theindole ringsystems
were planar, with dihedral angles of 1.49(11)° between rings A
(C2AC7) and B (N1/C1/C2/C7/C8) in dye 2, and 2.48(10)° and
1.56(10)° between rings: A (C2AC7) and B (N1/C1/C2/C7/C8), A0
(C20AC70) and B0 (N10/C10/C20/C70/C80) in dye 4. In the closely related
compounds, 3-(4-chlorophenyldiazenyl)-1-methyl-2-phenyl-1H-
indole
5 [29], N-{4-[(2-phenyl-1H-indol-3-yl)-diazenyl]phenyl}
acetamide 6 [30], 5-(4-ethoxyphenyldiazenyl)-8-hydroxyquinoline
7 [31], 2-phenyl-3-(5-ethyl-1,3,4-thiadizol-2-yldiazenyl)-1H-indole
8 [32], ethyl[2-(2-phenyl-1H-indol-3-yldiazenyl)-1,3-thiazol-4-yl]
region. For dye 2,
Dkmax is 32 nm in methanol + HCl relative to
methanol; similarly for dye 3
relative to methanol.
D
kmax is 38 nm in methanol + HCl
acetate
9 [33], ethyl 2-{[(2-phenyl-1H-indol-3-yl)diazenyl]thi-
azol-4-yl}acetate 10 [34], 1-methyl-2-phenyl-3-(1,3,4-thiadiazol-

320
Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
Fig. 3. (a) The molecular structure of dye 2, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level [40]. Hydrogen bonds are
shown as dashed lines. (b) A partial packing diagram of dye 2 [40].
2-yldiazenyl)-1H-indole 11 [35], 1,2-dimethyl-3-(thiazol-2-
yldiazenyl)-1H-indole 12 [36], 3-(5-ethyl-1,3,4-thiadiazol-2-
yldia-zenyl)-1-methyl-2-phenyl-1H-indole 13 [37] and 3-(6-meth-
oxybenzothiazol-2-yldiazenyl)-1-methyl-2-phenyl-1H-indole 14
[38], the observed A/B and/or A0/B0 dihedral angles were 1.56(11)°
and 0.77(12)° in 5, 1.63(14)° in 6, 1.60(14)° in 7, 2.28(9)° and
1.32(11)° in 8, 0.99(10)° in 9, 0.59(7)° in 10, 4.26(7)° in 11,
0.59(12)° in 13 and 1.16(7)° in 14. The orientations of rings C
(C11AC16) (in dye 2) and C (C10AC15), D (C16AC21) and C0
(C100AC150), D0 (C160AC210) (in dye 4) with respect to the indole ring
systems might be described by the dihedral angles of 4.58(12)° (for
dye 2) and 44.28(8)°, 12.77(7)°, 47.80(7)° and 11.94(7)° (for dye 4),
respectively.
they are oriented with respect to the indole ring system at dihedral
angles of 1.22(11)° and 1.49(11)°, respectively. In the crystal struc-
ture, the molecules are elongated along the a-axis and stacked
along the c-axis. In dye 4, intramolecular CAHꢃ ꢃ ꢃN hydrogen bonds
(Fig. 4a, Table 5) result in the formations of non-planar and planar
six-membered rings:
E
(N2/N3/C1AC3/H3) and E0 (N20/N30/
C10AC30/H30), respectively, in which ring E0 is oriented with respect
to the indole ring system at a dihedral angle of 0.42(5)°. Ring E
adopts envelope conformation with atom N3 displaced by
ꢁ0.180(2) Å from the plane of the other ring atoms.
In the crystal structure, intermolecular CAHꢃ ꢃ ꢃO hydrogen
bonds (Table 5) link the molecules into infinite chains along the
c-axis (Fig. 4b).
The phenyl rings are rotated around the C8AC10 and C80AC100
(in dye 4) bonds with the corresponding torsion angles of
Computational analysis
N1AC8AC10AC15
[ꢁ139.3(2)°]
and
N10AC80AC100AC150
[131.8(2)°]. The molecules of dyes 2 and 4 have trans geometries
about the azo linkages and the torsion angles of the central
ACAN@NACA are 178.7(3)° [C1AN2AN3AC11] (for dye 2) and
178.64(19)° [C1AN2AN3AC16] and 179.8(2)° [C10AN20AN30AC160]
(for dye 4).
The most stable structures for dyes 1–4 were obtained from the
potential energy surface (PES) scan using HF/6-31G(d) method and
reoptimized at the DFT level using the B3LYP/6-311+G(d,p).
The model compounds (dye 2 and 4) can be only azo form be-
cause of no intermolecular proton transfer whereas dye 1 and 3
can show the azo–hydrazone tautomerism. To compare the stabil-
ity of the azo and hydrazone forms of dye 1 and dye 3, each forms
of dyes are optimized in gas-phase and different solvents such as
In dye 2 (Fig. 3a), intramolecular CAHꢃ ꢃ ꢃN hydrogen bonds (Ta-
ble 4) result in the formations of planar six- and five-membered
rings: D (N2/N3/C1AC3/H3) and E (N2/C1/C8/C9/H9B), in which
Fig. 4. (a) The molecular structure of dye 4, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level [40]. Hydrogen bonds are
shown as dashed lines. (b) A partial packing diagram of dye 4 [40].

Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
321
Table 3
The calculated and experimental values of selected bond lengths (Å) and angles (°) with the torsion angles (°) for dyes 1–4. For dye 4, the torsion angle values in the parenthesis
are for the other conformation with the energy value ꢁ1127.63646172 a.u. and for the other of two crystallographically independent molecules obtained by X-ray
crystallography.
Parameters
Dye 1
Calc.
Dye 2
Calc.
Parameters
Dye 3
Calc.
Dye 4
Calc.
Exp.
Exp.
Bond lengths
O1AC17
N1AC7
N1AC8
N2AC1
Bond lengths
O1AC22
N1AC7
N1AC8
N2AN3
N2AC1
N3AC16
C8AC10
Bond angles
N3AN2AC1
N2AN3AC16
N2AC1AC2
N2AC1AC8
N1AC8AC10
C8AN1AC7
Torsion angles
C1AN2AN3AC16
N1AC8AC10AC11
N1AC8AC10AC15
N2AN3AC16AC21
N2AN3AC16AC17
C8AC1AN2AN3
1.218
1.393
1.366
1.373
1.267
1.414
1.219
1.397
1.370
1.371
1.268
1.413
1.175(6)
1.315(5)
1.313(5)
1.354(5)
1.248(5)
1.405(5)
1.218
1.389
1.371
1.268
1.372
1.413
1.464
1.219
1.394
1.375
1.268
1.371
1.414
1.470
1.208(3)
1.392(3)
1.365(3)
1.275(3)
1.385(3)
1.418(3)
1.471(3)
N2AN3
N3AC11
Bond angles
C8AN1AC7
N3AN2AC1
N2AN3AC11
N2AC1AC8
C2AC1AN2
C2AC1AC8
C1AC2AC7
Torsion angles
C1AN2AN3AC11
N2AN3AC11AC12
N3AN2AC1AC2
N2AC1AC8AC9
C9AC8AN1AC7
110.4
115.9
114.6
120.1
132.3
107.6
106.1
109.3
115.9
114.7
120.3
132.2
107.5
105.8
105.7 (4)
119.4 (4)
116.3 (3)
122.6 (4)
131.2 (4)
106.1 (4)
104.8 (4)
115.9
114.3
131.5
120.9
120.8
110.6
116.1
114.2
131.9
120.5
123.3
109.2
113.6(2)
113.1(2)
131.7(2)
120.3(2)
122.7(2)
109.0(2)
179.9
179.9
0.0
0.0
180.0
180.0
180.0
0.0
0.0
180.0
178.7(3)
175.7(4)
0.0(7)
0.0(7)
178.5(4)
178.2
ꢁ32.0
147.0
170.4
ꢁ10.8
178.5
ꢁ178.9(179.0)
50.8(ꢁ50.8)
178.64(19)(179.8(2))
42.6(3)(ꢁ48.6(3))
ꢁ139.3(2)(131.8(2))
ꢁ174.2(2)(170.0(3))
4.2(4)(ꢁ9.7(4))
ꢁ130.9(130.9)
ꢁ174.4(174.4)
6.2(ꢁ6.2)
ꢁ179.1(179.1)
ꢁ174.3(2)(178.1(2))
Table 4
Hydrogen bond geometry (Å, °) for dye 2.
D
E = 4.82 kcal/mol,
DG = 5.11 kcal/mol for dye 1 and DE =
4.80 kcal/mol, G = 4.25 kcal/mol for dye 3 in gas-phase. Further-
D
DAHꢃ ꢃ ꢃA
DAH
Hꢃ ꢃ ꢃA
2.55
2.59
Dꢃ ꢃ ꢃA
3.016(5)
2.976(6)
DAHꢃ ꢃ ꢃA
111
104
more, the relative energy values indicate that the stability of azo
form of each dyes does not change with respect to the interaction
of the solvent with the molecules. These results are in compatible
with the experimental results indicating that dyes 1 and dye 3 are
predominantly in azo form in used solvents.
C3AH3ꢃ ꢃ ꢃN3
0.93
0.96
C9AH9Bꢃ ꢃ ꢃN2
Table 5
The calculated and experimental values of selected bond
lengths, bond angles and important torsion angles for the dyes 2
and 4 are given in Table 3. However, the values are also given for
dyes 1 and 3 to compare with the corresponding model com-
pounds, i.e. dyes 2 and 4. It is found that the optimized geometry
of dye 2 were found to be consistent with the X-ray crystal struc-
ture results. C1AN2AN3AC11 torsion angle is obtained as 180.0°
from the optimization and 178.7(3) from the experimental results.
The optimized geometry of the dye 1 were also planar and the tor-
sion angle C1AN2AN3AC11 is obtained as 179.9°.
Hydrogen bond geometry (Å, °) for dye 4.
DAHꢃ ꢃ ꢃA
DAH
Hꢃ ꢃ ꢃA
Dꢃ ꢃ ꢃA
3.069(3)
3.037(3)
3.266(3)
3.457(3)
DAHꢃ ꢃ ꢃA
C3AH3ꢃ ꢃ ꢃN3
C30AH30ꢃ ꢃ ꢃN30
C9AH9Cꢃ ꢃ ꢃO10
0.93
0.93
0.96
0.96
2.61
2.57
2.54
2.55
111
111
133
157
i
C90AH9Dꢃ ꢃ ꢃO1ii
Symmetry code: (i) x + 1, ꢁy + ½, z ꢁ ½, (ii) x, ꢁy + ½, z ꢁ ½.
DMSO, chloroform, methanol and acetic acid. The obtained relative
stability from the total energies ( E) and the sum of electronic and
thermal free energies ( G) are given Table 6. The results indicate
For dye 4, two stable conformations were obtained as a result of
PES scan with the total energy of ꢁ1127.63646170 a.u. and
ꢁ1127.63646172 a.u. (Fig. 5). It has been observed that there no
D
D
that the azo form is more stable than the hydrazone form with
Table 6
The relative energies for the azo (a) and hydrazone (h) forms of the dyes 1 and 3.
Dye 1
D
Ea (kcal/mol)
Gb (Hartree)
D
Gb (kcal/mol)
Dye 3
D
Ea (kcal/mol)
Gb (Hartree)
D
Gb (kcal/mol)
Gas phase
DMSO
a
h
0
4.82
ꢁ896.30314
0
5.11
a
h
0
4.80
ꢁ1088.036652
ꢁ1088.029873
ꢁ1088.053594
ꢁ1088.047154
0
4.25
ꢁ896.294992
a
h
0
4.50
ꢁ896.320768
ꢁ896.311764
0
5.65
a
h
0
3.80
0
4.04
Chloroform
Methanol
A.Acid
a
h
0
4.68
ꢁ896.315377
ꢁ896.309195
ꢁ896.320509
ꢁ896.31154
ꢁ896.316781
ꢁ896.309124
0
3.88
a
h
0
4.22
ꢁ1088.04789
ꢁ1088.04134
ꢁ1088.053226
ꢁ1088.046797
ꢁ1088.049083
ꢁ1088.042672
0
4.11
a
h
0
4.51
0
5.63
a
h
0
3.82
0
4.03
a
h
0
4.64
0
4.80
a
h
0
4.13
0
4.02
a
The relative energy from the total energy.
The sum of the electronic and thermal free energy of the geometrically optimized dye structure using DFT calculations.
b

322
Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
E= -1127.63646170 a.u
E= -1127.63646172 a.u.
Fig. 5. Two conformers of dye 4 with the total energy of ꢁ1127.63646170 a.u. and ꢁ1127.63646172 a.u.
Table 7
Experimental and calculated absorption maxima (kmax) with parenthesized oscillator strength (f) for dyes 1–4.
kmax (nm)
DMSO
Exp.
Methanol
Exp.
A.Acid
Exp.
Cloroform
Exp.
Calc.
Calc.
Calc.
Calc.
Dye 1
Dye 2
Dye 3
Dye 4
409
413
430,530
417
410(1.001)
417(1.081)
433(0.797)
428(0.932)
402
408
422
408
408(0.978)
415(1.057)
431(0.778)
425(0.909)
409
414
421
414
407(0.986)
414(1.066)
430(0.791)
425(0.919)
397
408
417
413
409(1.004)
416(1.083)
432(0.808)
426(0.936)
Table 8
Experimental and theoretical 1H isotropic chemical shifts (in ppm) for dyes 1–4 calculated using the GIAO-B3LYP with 6-311+G(d,p) basis set.
Atom no.
Dye 1
Exp.
Dye 2
Exp.
Atom no.
Dye 3
Exp.
Dye 4
Calc.
Calc.
Calc.
Exp.
Calc.
H3
H4
H5
H6
7.41(d, 1H)
7.20(m, 2H)
7.20(m, 2H)
8.39(d, 1H)
2.68(s, 3H)
7.90(d, 2H)
8.11(d, 2H)
8.11(d, 2H)
7.90(d, 2H)
2.80(s, 3H)
9.00
7.65
7.66
7.67
3.03
8.40
8.35
8.59
8.37
2.00
3.06
3.06
8.41
7.58(d, 1H)
7.30(m, 2H)
7.30(m, 2H)
8.43(d, 1H)
2.61(s, 3H)
7.90(d, 2H)
8.10(d, 2H)
8.10(d, 2H)
7.90(d, 2H)
2.80(s, 3H)
2.80(s, 3H)
2.80(s, 3H)
3.81(s, 3H, ANCH3)
8.93
7.69
7.73
7.76
2.99
8.38
8.36
8.63
8.29
2.04
3.00
3.00
3.89
H3
H4
H5
H6
7.3(m, 2H)
9.14
7.70
7.71
7.87
8.23
8.00
7.93
7.91
8.70
8.16
8.55
8.51
8.45
2.75
8.67
7.4(m, 2H)
7.6(d, 2H)
7.6(d, 2H)
8.52(d, 1H)
9.17
7.79
7.76
7.81
7.93
8.04
8.03
8.03
8.32
7.86
8.48
8.43
8.38
2.71
7.51(m, 2H)
7.51(m, 2H)
8.51(d, 1H)
8.21(d, 2H)
7.64(m, 2H)
7.3(m, 2H)
7.64(m, 2H)
8.21(d, 2H)
7.90(d, 2H)
8.12(d, 2H)
8.12(d, 2H)
7.90(d, 2H)
2.65(s, 3H)
H9
H10
H11
H12
H13
H14
H16
H17
H19
H20
H22
NAR
7.72–7.80(m, 6H)
7.72–7.80(m, 6H)
7.40(m, 2H)
7.72–7.80(m, 6H)
7.72–7.80(m, 6H)
7.72–7.80(m, 6H)
8.08(d, 2H)
8.08(d, 2H)
7.72–7.80(m, 6H)
2.62(s, 3H)
H11
H12
H14
H15
H17
H17
H17
NAR
2.80(s, 3H)
2.80(s, 3H)
12.20(brs, NH indole)
12.52(brs, NH indole)
3.88(s, 3H, ANCH3)
3.87
s: singlet d: doublet, m:multiplet, brs: broad singlet.
0.014 Å for dye 4 in bond lengths. The largest difference observed
in C8AN1AC7 is 3.6° for dye 2 and in N3AN2AC1 is 2.5° for dye 4.
The calculated N@N distance are obtained as 1.268 Å for both of
them. However, X-ray data show that they are double bond charac-
ter with the value of 1.248(5) Å for dye 2 and 1.275(3) Å for dye 4.
It is seen that the experimental and calculated results are good
agreement with each other. It is also obtained that the double bond
character are seen for dyes 1 and 3 with the values 1.267 Å and
1.268 Å, respectively. It is noted that there is no experimental re-
sults of crystal structures parameters for dyes 1 and 3. Therefore,
we have calculated the maximum absorption peaks (kmax) at opti-
mized geometries and compared with experimental data.
From the optimized geometry, maximum absorption wave-
length (kmax) and corresponding oscillator strengths (f) have been
calculated, for each dye, using TD-DFT with the B3LYP/6-
311g(d,p) level of theory with DMSO, chloroform, methanol and
acetic acid. The theoretical and experimental maximum absorption
wavelengths are compared in Table 7. It is obtained that the calcu-
differences between bond lengths and bond angles whereas the
differences between torsion angles are seen for two conformations.
The selected values obtained from the optimized geometry with
the total energy of ꢁ1127.63646170 a.u. and also experimental re-
sults are given in Table 3. The selected torsion angle values in the
parenthesis are for the other conformation with the energy value
ꢁ1127.63646172 a.u. and for the other of two crystallographically
independent molecules obtained by X-ray crystallography. The tor-
sion angle N1AC8AC10AC15 is ꢁ130.9° and 130.9° for two confor-
mations and corresponding X-ray results are ꢁ139.3(2)° and
131.8(2)°, respectively. Both of the conformers have planar
structure. For one of them, C1AN2AN3AC16 torsion angle is
ꢁ178.96° and for the other 179.0° and corresponding X-ray results
are 178.64(19) and 179.8(2), respectively. This value is 178.2°
for dye 3.
The differences between the calculated and experimental val-
ues are found in the interval 0.001–0.082 Å for dye 2 and 0.001–

Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
323
Table 9
The in vitro antibacterial and antifungal activity of synthesized dyes against some microorganisms.
Microorganisms
Diameter of zone (mm)
Dye1
Dye2
Dye3
Dye4
SAM
CN
SXT
MCZ
S. aureus
S. aureus
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
4
2
–
–
–
–
2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
6
2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
4
2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
–
–
–
–
–
–
6
–
2
20
10
8
10
8
–
–
22
–
–
–
–
–
–
–
–
–
–
30
20
20
20
10
12
–
24
–
14
24
–
6
16
6
20
6
16
20
8
20
18
16
18
18
16
18
22
18
20
22
18
–
20
–
–
–
–
18
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
4
2
–
S. saprophyticus
S. saprophyticus
L. monocytogenes
L. innocua
P. aeruginosa
P. aeruginosa
P. aeruginosa
P. aeruginosa
P. putida
P. putida
Esherichia coli
E. coli
E. coli
E. coli
E. coli
K. pneumoniae
K. pneumoniae
Enterobacter sakazakii
E. sakazakii
Candida albicans
Candida albicans
Candida tropicalis
–
–
–
–
–
–
6
–
–
–
–
– no activity against to the microorganisms.
lated kmax values and corresponding oscillator strengths values did
not change significantly in all the employed solvents and did not
correlate with the polarity of the solvent. The calculated values
are quite close to the experimental results and the maximum dif-
ferences between experimental and calculated values are 10 nm
for dye 1, 7 nm for dye 2, 14 nm for dye 3 in choloroform and
17 nm for dye 4 in methanol. However, experimentally, the
absorption maxima shows little bathocromic shift with increasing
dielectric constant for the model compounds (dye 2 and 4). The
same trend is observed for dye 2 with the value of 1 nm and for
dye 4 with 2 nm in DMSO with respect to the value in chloroform
from theoretical calculations. Dyes 1 and 3 exhibit bigger change
according to their model compounds. While the experimental re-
sults show the difference values between DMSO and chloroform
are 12 nm and 13 nm for dyes 1 and 3, respectively, only 1 nm is
obtained from the theoretical calculations for each dyes.
at 12.20 and 12.52 ppm, respectively, can be assigned to indole
NAH which indicates azo tautomeric form.
The antimicrobial activities of the synthesized dyes
The antimicrobial activity of some of the azo dyes has been re-
ported previously [19,41,42].
Recently, it was synthesized different phenylazoindole dyes and
screened for their antimicrobial activities on Bacillus thuringiensis,
Bacillus subtilis, Bacillus megaterium, Proteus vulgaris, Pseudomonas
aeruginosa, Staphylococcus aureus, Escherichia coli and Saccharomy-
ces cerevisiae [19]. The dyes have showed remarkable activity
against B. megaterium, B. subtilis, B. thuringiensis and S. aureus, they
did not exhibit any activity against P. vulgaris. The dyes have
showed biological activity on the Gram positive rather than the
Gram negative bacteria. However, Pseudomonas sp. E. coli and
Staphylococcus sp. showed resistance to most of these compounds,
this could be probably due to the R plasmid that is present in them
[19].
Chemical shifts
The calculated 1H NMR chemical shifts for the dyes 1–4 to-
gether with the corresponding experimental values with the num-
bering in Scheme 1 are shown in Table 8. Since experimental
1H chemical shift values were not available for individual hydro-
gen, the average values for CH3 hydrogen atoms are presented.
As can be seen from Table 8, calculated 1H chemical shift values
of the dyes are generally agreement with the experimental data.
The 1H NMR spectra measured in DMSO-d6 for the dyes 1 and 2
showed a singlet peak at 2.68 and 2.61 ppm for indole CACH3
respectively. Corresponding calculated values are 3.06 ppm and
2.99 ppm for the dyes 1 and 2, respectively. A broad singlet peak
for indole NAH at 12.20 ppm (calc. 8.41 ppm) for dye 1 and a
singlet peak appeared at 3.81 ppm (calc. 3.89 ppm) for indole
NACH3 for dye 2. Similarly, a broad singlet peak for indole NAH
at 12.52 ppm (calc. 8.67 ppm) for dye 3 and a singlet peak ap-
peared at 3.88 ppm (calc. 3.87 ppm) for indole NACH3 for dye 4.
Generally, NAH proton of hydrazone tautomer appears after
14 ppm values [39]. According to our results, the 1H NMR spectra
of dyes 1 and 3 show one signal in DMSO, where the broad signal
The antimicrobial activity of seventeen azo disperse dyes
against Bacillus thuringiensis and Escherichia coli are investigated
[41]. The novel mordant and disperse azo dyes were synthesized
and antimicrobial activity of these dyes against Escherichia coli,
Staphylococcus aureus, Salmonella typhi, Bacillus subtilis were stud-
ied [42]. However, until now, no systematic study has been under-
taken to examine the antimicrobial properties of phenylazoindole
based dyes. For this reason, in the current investigation, different
microorganisms have been chosen and the antimicrobial effect of
indole dyes on these microorganisms under in vitro conditions
has been studied. The antibacterial and anti-fungal activities of
the dyes were determined against 21 bacteria (2 Staphylococus aur-
eus, 2 S. saprophyticus, 1 Listeria monocytogenes, 1 L. innocua, 4 Pseu-
domonas aeruginosa, 2 P. putida, 5 Escherichia coli, 2 Klebsiella
pneumoniae, 2 Enterobacter sakazakii) and three yeast. The data
for the antimicrobial tests are summarized in Table 9.
It was generally observed that the dyes were low or no active
against test microorganisms. The highest inhibition of growth oc-
curred in dye 2 against Candida albicans and dye 4 against Candida

324
Z. Seferog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 314–324
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Conclusions
As a result, new series phenylazoindole dyes were synthesized
and characterized in this study. The most stable tautomeric form
of these dyes were determined easily by using model compounds
(dye 2 and 4) in solution and solid state. All spectroscopic data
showed that the azo form is predominant for dyes 1 and 3. The
experimental data are compared with theoretical values and it
was found that the calculation results are in very good agreement
with the experimental data. Microorganisms (e. g. bacteria, fungi)
have different cell wall structure and plasmids. Plasmids carry
genes that may benefit survival of the microorganism (like antibi-
otic resistance). Dyes using in the research were low and no active
against test microorganisms, this could be due to plasmid that is
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Acknowledgement
[31] Z. Seferog˘lu, T. Hökelek, E. Sßahin, A. Saylam, N. Ertan, Acta Crystallogr. E 62
(2006) 4130–4131.
The theoretical part of this work is supported by a grant from
Gazi University (BAP: 18/2011-06).
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