Novel acid mono azo dye compound: Synthesis, characterization, vibrational, optical and theoretical investigations of 2-[(E)-(8-hydroxyquinolin-5-yl)- diazenyl]-4,5-dimethoxybenzoic acid

Article abstract of DOI:10.1016/j.saa.2012.05.068

Novel acid mono azo dye, 2-[(E)-(8-hydroxyquinolin-5yl)-diazenyl]-4,5- dimethoxybenzoic acid (HQD), was synthesized by coupling diazonium salt solution of 2-amino-4,5-dimethoxybenzoic acid (DMA) with 8-hydroxyquinoline (HQ). This dye was characterized by

Full text of DOI:10.1016/j.saa.2012.05.068

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Novel acid mono azo dye compound: Synthesis, characterization, vibrational,
optical and theoretical investigations of 2-[(E)-(8-hydroxyquinolin-5-yl)-
diazenyl]-4,5-dimethoxybenzoic acid
b
a
b
c
Mustafa Saçmacı a, , Hatice Kanbur Çavußs , Hatice Arı , Recep Sßahingöz , Talat Özpozan
⇑
a Bozok University, Faculty of Arts and Sciences, Department of Chemistry, Yozgat, Turkey
b Bozok University, Faculty of Arts and Sciences, Department of Physics, Yozgat, Turkey
c Erciyes University, Faculty of Sciences, Department of Chemistry, Kayseri, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
"
"
A novel azo dye (HQD) was
synthesized and characterized by
spectroscopic methods.
Optical–vibrational properties were
determined by experimentally and
theoretically.
The azo tautomeric form of HQD was
found to be more stable than
hydrazone form.
Two important hydrogen bondings
were determined as intramolecular
interactions.
HO
HO
O
N
O
O
H
H
H3CO
H
NH2
O
H
3CO
N
H
3CO
H3CO
N
HQ
N
O
N
O
3CO
NaNO /HCl
2
H3CO
H
N
OH
N
Hydrazone form of HQD
Azo form of HQD
DMA
The azo form and hydrogen bondings
were supported by calculations and
measurements.
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel acid mono azo dye, 2-[(E)-(8-hydroxyquinolin-5yl)-diazenyl]-4,5-dimethoxybenzoic acid (HQD),
was synthesized by coupling diazonium salt solution of 2-amino-4,5-dimethoxybenzoic acid (DMA) with
8-hydroxyquinoline (HQ). This dye was characterized by UV–vis, IR & Raman, 1H and 13C NMR spectro-
scopic techniques and elemental analysis. The normal coordinate analysis of HQD was also performed to
assign each band in vibrational spectra. DFT (B3LYP and B3PW91) calculations were employed to opti-
mize the geometry, to interpret NMR spectra, to calculate and to determine the stable tautomeric struc-
ture of the compound. Natural Bond Orbital (NBO) analysis was performed to investigate intramolecular
interactions. The vibrational spectral data obtained from solid phase IR & Raman spectra were assigned
based on the results of the theoretical calculations. UV–vis spectroscopic technique was employed to
obtain the optical band gap of HQD. The analysis of the optical absorption data revealed the existence
of direct and indirect transitions in the optical band gaps. The optical band gaps of HQD have been found
1.95 and 1.90 eV for direct and indirect transitions, respectively.
Received 10 February 2012
Received in revised form 26 May 2012
Accepted 29 May 2012
Available online 09 June 2012
Keywords:
Azo dye
Azo-hydrazone tautomerism
Vibrational analysis
Geometry optimization
DFT
Optical properties
Published by Elsevier B.V.
Introduction
been carried out in recent years on the synthesis and spectroscopic
properties of this group of dyes [4–6]. The photo-physical and
Aromatic azo dyes are the most widely used class of coloring
materials due to their massive application in various fields of sci-
ence and technology [1–3]. A large amount of investigation has
photo-chemical properties of this class of dyes make them suitable
as optical sensors and advanced materials [7]. Furthermore, azo
compounds are known to be involved in a number of biological
reactions such as inhibition of DNA, RNA, and protein synthesis, car-
cinogenesis, and biological activity against bacteria and fungi [8,9].
The azo dyes produced by diazotization of aromatic amines and
⇑
Corresponding author. Tel./fax: +90 354 2421021/22.
E-mail address: msacmaci@hotmail.com (M. Saçmacı).
1386-1425/$ - see front matter Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2012.05.068

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
89
-
+
Cl
NH
N
N
2
H CO
3
H CO
3
NaNO /HCl
2
o
OH
OH
C
0 - 5
H CO
3
H CO
3
O
O
Diazonium Salt
DMA
OH
N
KOH
H
HQ
O
O
O
O
H
H
H CO
N
3
N
H CO
3
N
O
N
O
H CO
3
H CO
H
3
N
N
Azo - form of HQD
Hydrazone - form of HQD
Scheme 1. Synthetic routes for the preparation of HQD.
Fig. 1. Stable conformers of two tautomers for HQD.

90
M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Table 1
Reagents and solutions
Energies and relative energies of azo and hydrazone form of HQD.
The standard chemicals 8-hydroxyquinoline, sodium nitrite,
concentrated hydrochloric acid, ethanol 96% (E. Merck, Darmstadt,
Germany) and 2-amino-4,5-dimethoxybenzoic acid (Alfa Easer,
MA, USA) were used without any further purification.
Conf.
B3LYP/6-311G(d)
B3PW91/6-311G(d)
Energy (kcal/
mol)
D
mol)
E (kcal/
Energy (kcal/
mol)
D
mol)
E (kcal/
Azo form
Hydrazone
form
ꢀ775317.2986 0.0000
ꢀ775315.1226 2.1760
ꢀ775008.4011 0.0000
ꢀ775005.5914 2.8097
Preparation of 2-[(E)-(8-hydroxyquinolin-5-yl)diazenyl]-4,
5-dimethoxybenzoic acid (HQD)
Hydrochloric acid solution (23 mL, 1.60 M) was added to 2-ami-
no-4,5-dimethoxybenzoic acid (2.0 mL, 1.0 mmol). The resulting
mixture was stirred and cooled to 0 °C to which a solution of so-
dium nitrite (0.07 mg, 1.0 mmol, in 15 mL of water) was added
drop wise. The so-formed diazonium chloride was consecutively
coupled with an alkaline solution of 8-hydroxyquinoline
(0.15 mg, 1.0 mmol) in 20 mL of ethanol containing 60.2 mg
(1.0 mmol) of potassium hydroxide. The red precipitate formed
immediately was filtered and washed several times with ethanol-
water mixture. The crude product obtained was purified by recrys-
tallization from hot ethanol (yield 75%). M.p.: 270 °C. The reaction
is shown in Scheme 1. Anal. Calc. for C18H15N3O5: C, 61.19; H, 4.28;
N, 11.89. Found: C, 60.95; H, 4.35; N, 11.70.
their carboxy derivatives containing at least one azo group (–N@N–
) attached to at least one aromatic moiety are the most widely used
dyes in textile, printing, leather, papermaking, drug and food indus-
tries [10]. The azo/hydrazone tautomerism in azo compounds is
very attractive from theoretical and practical viewpoints and has
been of particular interest [11–13]. It is described by the intramo-
lecular proton transfer between the phenol and imine groups in
ground and/or excited state [14]. The presence of azo/hydrazone
tautomerism in these compounds may influence considerably in
their unique photo-physical and photo-chemical properties, which
is turn strongly influenced by several factors including tempera-
ture, the substituent structure and solvent polarity [15–17].
In this study, a new mono azo reactive dye included in azo/
hydrazone tautomerism, named 2-[(E)-(8-hydroxyquinolin-5yl)-
diazenyl]-4,5-dimethoxybenzoic acid (HQD), was synthesized from
2-amino-4,5-dimethoxybenzoic acid (DMA) and 8-hydroxyquino-
line (HQ). The product was characterized with molecular spectro-
scopic techniques (UV–vis, IR & Raman, 1H and 13C NMR) and
elemental analysis. The optical band gap was measured through
UV–vis spectroscopic measurements and confirmed by theoretical
calculations of absorption maxima of the UV–vis spectrum of HQD.
Theoretical DFT (B3LYP and B3PW91) calculations were also con-
ducted for spectral confirmations (NMR, vibrational, UV–vis) to
investigate the optimum geometry of the synthesized compound,
to see possible hydrogen bondings by Natural Bond Orbital (NBO)
analysis. NBO analysis has been used to elucidate the information
regarding charge transfer within the molecule. Normal coordinate
analysis (NCA) was also performed to assign vibrational bands ap-
peared in vibrational (IR & Raman) spectra.
Instrumentation
The melting point was determined on an Electrothermal 9200
apparatus, and is uncorrected. Mid and far IR spectra were re-
corded on a Perkin-Elmer Model 298 spectrophotometer, and the
Raman spectrum was recorded on an Agiltron Model portable
Raman spectrophotometer. 1H and 13C NMR spectra were recorded
on a Bruker Avance model using Si(CH3)4 as reference in DMSO-d6
at 400 MHz and 100 MHz, respectively. Elemental analysis (C, H, N)
was carried out using LECO-932 CHNS-O analyzer. The UV–vis
spectrum was recorded by the use of a Hach Lange DR 5000
UV-spectrophotometer.
Computational methods
All the calculations including geometry optimization,
conformer analysis and NBO analysis were performed using the
Gaussian 09 [18] by density functional (B3LYP and B3PW91) meth-
ods with 6-311G(d) basis set. Conformer analysis option was em-
ployed to obtain the most stable structure. NBO analysis has
been performed to examine the bonds forming molecule. Then,
the structure of the stable conformer was used in the so-called
NCA vibrational analysis. Potential Energy Distribution (PED) of
normal frequencies was calculated using the VEDA4 program
[19,20]. 1H and 13C NMR chemical shifts were calculated by the
Guage-Including Atomic Orbital (GIAO). The calculated vibrational
Experimental and computational methods
Experimental studies
HQD was synthesized and characterized by elemental analysis,
NMR, vibrational and UV–vis spectroscopic techniques as de-
scribed in the following sections.
Table 2
Selected optimized geometrical parameters of HQD in azo form.
Bond lengths (Å)
B3LYP
B3PW91
Bond angles (°)
B3LYP
B3PW91
Torsional angle (°)
B3LYP
0.1
0.0
179.6
ꢀ167.0
0.2
B3PW91
C1–C2
C1–H6
C3–C4
C4–N15
C8–N18
C9–O16
1.3749
1.0843
1.4181
1.3573
1.3942
1.3367
0.9769
1.2610
1.4102
1.3707
1.3693
1.2054
1.3386
0.9855
1.4359
1.0917
1.4364
1.3734
1.0849
1.4143
1.3532
1.3890
1.3306
0.9770
1.2579
1.4047
1.3650
1.3635
1.2042
1.3324
0.9874
1.4285
1.0925
1.4289
C1C2C3
C1C5N15
C2C1H6
C3C4C9
C4N15C5
C4C9O16
C9O16H17
C8N18N19
N15C5H10
N18N19C20
C22C28O29
C23O37C38
C26O32C33
C28O30H31
O29C28O30
O32C33H35
O37C38H39
119.4
122.9
120.9
120.2
117.9
118.6
106.2
116.7
116.6
116.8
121.1
115.4
115.4
109.5
121.4
105.9
105.9
119.3
123.0
120.9
120.3
117.9
118.3
105.8
116.6
116.6
116.7
121.1
115.0
115.1
109.2
121.6
106.0
106.0
C1C2C3C4
C1C5N15C4
C3C4C9O16
0.2
0.0
179.6
ꢀ167.0
0.2
C3C8N18N19
C4C9O16H17
C8N18N19C20
H14C12C8N18
N18N19C20C21
C20C21C23C26
C20C22C25C26
C20C22C28O29
C21C23O37C38
C22C28O30H31
C23C26O32C33
C23O37C38H39
C26O32C33H35
O29C28O30H31
ꢀ176.4
ꢀ176.5
O16–H17
N18@N19
N19–C20
0.4
0.4
9.2
0.8
0.6
9.9
0.9
0.7
C
C
C
C
23–O37
26–O32
28–O29
28–O30
ꢀ177.6
113.9
ꢀ1.1
ꢀ178.3
114.6
ꢀ0.9
O
O
30–H31
32–C33
ꢀ69.4
179.9
ꢀ179.9
179.3
ꢀ68.4
179.8
ꢀ179.8
ꢀ179.4
C
O
33–H34
37–C38

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
91
Table 3
Intramolecular hydrogen bonding parameters based on B3PW91/6-311G(d) basis set of HQD.
Bond
A–Hꢁ ꢁ ꢁB (°)
Bond
Hꢁ ꢁ ꢁB (Å)
Bond
Aꢁ ꢁ ꢁB (Å)
Bond
A–H (Å)
O
O
30–H31ꢁ ꢁ ꢁN19
150.25
117.81
98.12
116.57
115.89
H31ꢁ ꢁ ꢁN19
H17ꢁ ꢁ ꢁN15
H27ꢁ ꢁ ꢁO29
H41ꢁ ꢁ ꢁO32
H34ꢁ ꢁ ꢁO37
1.7340
2.0436
2.3739
2.4234
2.4578
N19ꢁ ꢁ ꢁO30
N15ꢁ ꢁ ꢁO16
O29ꢁ ꢁ ꢁC25
O32ꢁ ꢁ ꢁC38
O37ꢁ ꢁ ꢁC33
2.6372
2.6445
2.7454
3.0713
3.0951
O30–H31
O16–H17
C25–H27
C38–H41
C33–H34
0.9874
0.9770
1.0840
1.0920
1.0925
16–H17ꢁ ꢁ ꢁN15
C
C
25–H27ꢁ ꢁ ꢁO29
38–H41ꢁ ꢁ ꢁO32
C33–H34ꢁ ꢁ ꢁO37
A: H bonded electronegative atom, B: electronegative atom having lone pair electrons, A–H: proton donor group.
The total energies and the relative energies of two tautomers
are given in Table 1 which shows that the azo form is the most sta-
ble conformer. All the calculations were then followed using the
most stable structure of the azo form of HQD.
Selected bond lengths, bond angles and torsional angles of the
most stable structure of HQD in azo form calculated with the
methods of DFT (B3LYP and B3PW91) with 6-311G(d) basis set
were displayed in the Table 2.
HQD consists of two separate ring systems, the phenyl ring and
quinoline ring connected to each other by N@N bridge. The N@N
and N–C bond lengths in azobenzenes were found experimentally
within the range of 1.26–1.27 and 1.393–1.432 Å, respectively [21]
because of conjugation with phenyl ring. The bond length calcu-
lated for N18@N19 at B3LYP level is 1.2610 Å, and at B3PW91 level
is 1.2579 Å. The bond lengths calculated for C8–N18 at B3LYP level
is 1.3942 Å, and at B3PW91 level is 1.3890 Å and for N19–C20 at
B3LYP level is 1.4102 Å, and at B3PW91 level is 1.4047 Å. The quin-
oline and phenyl is essentially planar as seen from the torsional
angles (C3C8N18N19 and N18N19C20C21). The carboxyl group is also
planar, and lies in the same plane of quinoline ring, which can be
seen from the torsional angle (C22C28O30H31).
Table 4
Selected second-order perturbation energies E(2) (donor?acceptor).
Donor NBO
(i) electron
Acceptor NBO
(j) electron
E(2)a
(kcal/mol)
E(i) ꢀ E(j)b
F(i,j)c
(a.u)
(a.u.)
LP (1) N19
LP (1) N15
BD⁄(1) O30–H31
BD⁄(1) O16–H17
22.38
4.31
0.83
0.74
0.122
0.051
LP (1): Lone Pair electrons on electronegative donor atoms, BD⁄(1): antibonding
electrons.
r
a
E(2) means energy of hyperconjugative interactions (stabilization energy).
Energy difference between donor and acceptor i and j NBO orbitals.
F(i,j) is the Fock matrix element between i and j NBO orbitals.
b
c
wavenumbers and chemical shifts were compared with the exper-
imental data of HQD. Finally, absorption maxima for HQD in UV–
vis region were also calculated by the Configuration Interaction
Singles (CIS), Time-Dependent Density-Functional Theory (TD-
DFT) and Zerner’s Intermediate Neglect of Differential Overlap
(ZINDO) methods to confirm the experimentally measured absorp-
tion maxima.
Hydrogen bonding
Results and discussion
HQD displays a trans configuration of the azo moiety which
forms an intramolecular O–Hꢁ ꢁ ꢁN@N hydrogen bond. Bond lengths
and bond angles for the potential hydrogen bonds of the HQD com-
pound were shown in the Table 3. As it could be seen easily from the
list we may conclude that there is hydrogen bonding between
Conformational analysis and tautomerization of HQD
The geometry of the molecule was optimized by theoretical cal-
culations using B3LYP/6-311G(d) and B3PW91/6-311G(d) level of
theories. The most stable conformer was found as the azo form
by scanning the critical torsional angles for the energy calculations.
The critical torsional angles that can affect the stable conformer
structure of HQD were determined as T(C3C8N18N19), T(C4C9C16H17),
T(C8N18N19C20), T(N18N19C20C21), T(C20C22C28O29), T(C21C23O37C38),
T(C22C28O30H31), T(C23C26O32C33), T(C23C37C38H39) and T(C26O32
C33H35) angles as shown in Figs. S1–10 (Supplementary data S1–
10). Each torsional angle was scanned 20 times by rotating 18° each
time for the determination of torsional angle–relative energy
change and to plot this change graphically. Full optimization can
be achieved to obtain the most stable conformer by rotating these
torsional angles to calculate their energies. The most stable con-
former was obtained as the optimized geometry through scanning
all the critical angles. The possible structures of HQD with the
lowest energies of azo and hydrazone tautomers are shown in Fig. 1.
H31ꢁ ꢁ ꢁN19 when we take into account the value of the angle O30
–
H31ꢁ ꢁ ꢁN19 (between 130° and 170°) and the bond length of
H31ꢁ ꢁ ꢁN19 (between 1.5 and 2.2 Å). This hydrogen bonding can be
named as medium strength hydrogen bonding according to Jeffrey’s
classification [22] on basis of geometrical parameters. There is an-
other, relatively weaker, H-bonding between H17 and N15 atoms
in quinoline group. The other possible H-bonding interactions such
as H27ꢁ ꢁ ꢁO29, H41ꢁ ꢁ ꢁO32, and H34ꢁ ꢁ ꢁO37 had no significant importance
as expected from the geometrical configuration of HQD molecule.
NBO analysis
As an efficient method for studying intra- and intermolecular
bonding and interaction among bonds, NBO analysis was
Table 5
NBO results showing of Lewis and non-Lewis orbitals of HQD.
Bond (A–B)
BD O30–H31
ED/Energy (a.u)
EDA (%)
EDB (%)
NBO
0.875(sp2.88)O+
s (%)
p (%)
1.98513
ꢀ0.75302
0.06908
0.39810
1.98632
ꢀ0.75152
0.02453
0.36713
76.56
–
23.44
–
75.34
–
24.66
–
23.44
–
76.56
–
24.66
–
75.34
–
25.73
100.00
25.73
100.00
21.15
100.00
21.15
74.18
–
74.18
–
78.75
–
78.75
–
0.484(s)H
BD⁄ O30–H31
BD O16–H17
BD⁄ O16–H17
0.484(sp2.88)O+
ꢀ0.875(s)H
0.868(sp3.72)O+
0.497(s)H
0.497(sp3.72)O+
ꢀ0.868(s)H
100.00

92
M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Fig. 2. 1H NMR spectrum of HQD.
Fig. 3. 13C NMR spectrum of HQD.
performed to identify and explain possible formation of hydrogen
molecule can form between N19 atom of the azo group (N19@N18
and H31 atom of the COOH31 group (Fig. 1). According to the NBO
analysis, another weaker hydrogen bond interaction (O16
)
bondings on HQD (Tables 4 and 5). The stabilization energy E(2)
associated with hyperconjugative interaction n(N19) ? r⁄(O30
–
–
H
31) was obtained as 22.38 kcal/mol. Taking into account the rule
H17ꢁ ꢁ ꢁN15) was formed between the hydroxyl and nitrogen of the
quinoline group with 4.31 kcal/mol of stabilization energy.
From Table 5, it is evident that the ED in O30–H31 antibonding
r⁄ orbital was significantly increased (0.06908e) by the strong
‘‘the larger the stabilization energy E(2) value, the more intensive
is the interaction between electron donors and electron acceptors’’,
we may conclude that the strongest hydrogen bonding in the

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
93
Table 6
Calculated and experimental 13C and 1H NMR chemical shifts (ppm) for HQD.
Carbon
Calculated
B3LYP
Experimental
Proton
Calculated
B3LYP
Experimental
B3PW91
B3PW91
C28
C9
C23
C26
C5
C20
C8
C4
C2
C25
C3
C22
C1
170.47
162.70
161.44
160.50
151.95
151.07
143.43
141.12
137.45
134.11
132.34
128.64
128.50
119.75
113.46
103.18
59.47
169.82
162.20
160.49
158.10
149.23
149.12
139.99
136.72
133.90
129.58
127.79
124.97
124.33
116.16
110.17
102.77
57.96
168.58
158.17
151.72
150.90
149.51
145.32
139.25
138.39
132.66
127.66
124.34
123.83
116.83
112.21
111.91
100.42
56.42
H31
H17
H10
H7
H27
H14
H24
H6
11.81
10.12
8.77
8.54
7.92
7.70
7.58
7.55
7.13
3.70c
3.69c
12.01
10.27
8.92
8.67
7.98
7.80
7.75
7.64
7.29
3.77c
3.75c
12.80
11.08
9.31
8.98
7.88
7.76
7.47
7.35
7.23
3.94
3.68
H13
CH3
CH3
a
b
C12
C11
C21
C33
C38
59.08
57.78
56.30
a
b
c
CH3 group of H34, H35, H36
CH3 group of H39, H40, H41
Averaged chemical shift.
.
.
13
11
9
190
B3LYP
B3PW91
y = 0.8996x + 0.6500
R2 = 0.9868
B3LYP
B3PW91
y = 0.8862x + 0.6350
2 = 0.9863
170
150
130
110
90
y = 1.0185x + 2.9065
y = 1.0176x + 0.3755
R
R2 = 0.9917
R
2 = 0.9913
7
5
70
3
3
5
7
9
11
13
50
50
70
90
110
130
150
170
Exp. Chemical Shifts
Exp. Chemical Shifts
Fig. 4. Plot of the experimental versus the calculated 13C NMR chemical shifts
Fig. 5. Plot of the experimental versus the calculated 1H NMR chemical shifts (ppm)
obtained by B3LYP and B3PW91 methods.
(ppm) obtained by B3LYP and B3PW91 methods.
served at 11.08 and 12.86 ppm were most probably resulted from
intra H-bondings of OH protons with N atoms of azo group and
quinoline cycle. The weakening and broadening of this type of pro-
ton signals might be caused by dimer formations between two
hydroxyquinoline groups of two different molecules as mentioned
by Albrecht et al. [23]. HQD prepared from HQ and DMA may exist
in two possible tautomeric forms, namely azo and hydrazone
forms as depicted in Scheme 1. Recently, Saylam et al. and La Deda
et al. reported the structures of some azoquinoline dyes and
pointed out that the azo form existed in the crystal form [24–
26]. Important structural information about HQD was obtained
from the 1H and 13C NMR spectra. In the 13C NMR, there is no
detectable signal for the carbon of carbonyl group (C@O) at quino-
line ring for the hydrazone form. Also, two broad bands (OH sig-
nals) were determined from the azo form of HQD in the 1H NMR
spectrum. The signal for the N–H proton of HQD for the hydrazone
form was not observed in DMSO-d6.
hydrogen bond between hydroxyl group (O30–H31) and azo nitro-
gen (N19) in the molecule. The interaction between N19 and
H31–O30 leads to an increase in electron density (ED) of O–H anti-
bonding orbital. The increase of population in O–H antibonding
orbital weakens the O-H bond, which results in bond elongation
and appearing red shift of stretching frequency in IR spectrum.
NMR spectra
1H NMR spectrum
The principle features of the 1H NMR spectrum with the assign-
ments proposed on the basis of the numbering scheme given in
Fig. 2 are as follows:
The 1H NMR spectrum of aromatic protons (Ar–H) of HQD in the
quinoline and benzene rings appeared in the range of
9.31–7.23 ppm. The signals at 3.94 and 3.90 ppm are assigned to
the methoxy (OCH3) protons. HQD showed a broad peak at
11.08 ppm for OH proton of quinoline ring and a broad peak at
12.86 ppm for OH proton attached to carbonyl group of benzene
ring. The very weak and broad bands of two hydroxyl protons ob-
13C NMR spectrum
The principle features of the 13C NMR spectrum with the assign-
ments proposed on the basis of the numbering scheme given in
Fig. 3 are as follows:

94
M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Fig. 6. The calculated and the experimental IR spectra of HQD.
The singlet peaks at 56.42 and 56.30 ppm are due to the meth-
Vibrational spectra and NCA
oxy (OCH3) carbons. The signals at 158.17, 151.72, 150.90, 149.51,
145.32, 139.25, 138.39, 132.66, 127.66, 124.34, 123.83, 116.83,
112.21, 111.92, 100.52 ppm belong to aromatic carbons (C@C)
and the singlet peak at 168.58 ppm carbonyl carbon (C@O).
The theoretically calculated 1H and 13C NMR chemical shifts of
HQD have been compared with the experimental data in Table 6.
According to these results, the calculated chemical shifts are in
agreement with the experimental data. In order to compare the
experimental chemical shifts with the theoretically calculated val-
ues, the correlation graphics have been presented in Figs. 4 and 5.
The carbon and proton chemical shift correlation coefficients were
found to be 0.9913, 0.9917 (13C NMR) 0.9863, 0.9868 (1H NMR) for
B3LYP/6-311G(d) and B3PW91/6-311G(d), respectively.
Infrared and Raman spectra
Mid IR spectrum recorded between 450 and 4000 cmꢀ1 was ex-
tended to Far IR with the same spectrometer by recording the re-
gion 30–700 cmꢀ1 in a different measurement. Raman spectrum
was also measured between 350 and 3154 cmꢀ1. The calculated
and the experimental IR and Raman spectra of HQD are shown in
Figs. 6 and 7, respectively.
Vibrational analysis of HQD
The vibrational analysis of HQD was performed through VEDA4
program after the calculation of the frequencies by DFT (B3LYP and
B3PW91) methods. The experimental frequencies (IR & Raman)
and the calculated frequencies were given with their Potential En-
ergy Distribution (PED) obtained from VEDA4 program in Table 7
to assign the bands. HQD has 41 atoms possessing 117 vibrational
degrees of freedom which should be observed both in IR and
Raman spectra due to the low symmetry (C1) of the molecule.
The calculated chemical shift values in the unscaled form given
above are in good agreement with the experimental values mea-
sured. The %relative errors of the 13C NMR and 1H NMR chemical
shifts obtained are 4.30% for B3LYP, 2.43% for B3PW91 and 3.67%
for B3LYP, 3.42% for B3PW91, respectively.

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
95
Fig. 7. The calculated and the experimental Raman spectra of HQD.
The calculated vibrational spectrum has been compared with
the experimental ones and the assignments of the vibrational
bands have been proposed. The differences between the experi-
mental and the theoretical frequencies are due, in part, to the fact
that the theoretical spectrum is obtained in the gas phase; how-
ever, the experimental spectra were measured in the solid phase.
Some of the intermolecular interactions were neglected in the nor-
mal coordinate calculations of the molecule but the NBO analysis
was carried out to see the intramolecular H-bondings in the
structure.
In MID IR spectrum of HQD there are two OH stretching bands
at 3408 and 3163 cmꢀ1 for OH of quinoline at 8th position and OH
of benzoic acid, respectively. The effect of intramolecular
H-bonding between the H31 atom of the carboxyl group and the
N19 atom of the azo group (Fig. 1) can be seen through decreasing
in wavenumber down to 3163 cmꢀ1. On the other hand, the rela-
tively weaker intramolecular H bonding between the OH hydrogen
at the 8th position of quinoline and the N atom of the quinoline
ring seemed not to be affected much with the OH stretching fre-
quency appeared at 3408 cmꢀ1, for which Teimouri et al. [27] ob-
served the similar OH stretching frequency of hydroxyquinoline
at 3434 cmꢀ1 and Krishnakumar and Ramasamy [28] found the
same OH band of 8-hydroxyquinoline at 3418 cmꢀ1. Considering
the position of OH bands, one can also conclude that the azo form
is supported by the vibrational spectrum. The aromatic C–H bands
were observed at 3120–3008 cmꢀ1 as usual and the methyl C–H
vibrations of methoxy group were observed at 2995–2841 cmꢀ1
.
This indicates that the C–H vibrations appeared at relatively higher
frequencies than the normal aliphatic C–H vibrations of paraffines
as a result of stronger C–H bonds in methoxy groups caused by
oxygen atoms making C atoms more electropositive. The single
stretching vibrations of carbonyl group appeared at 1726 cmꢀ1 also
supports azo form when compared with the two carbonyl groups
of hydrazone form. The strong bands at 1561 and 1503 cmꢀ1 were
assigned to C@N (ring) and N@N stretching vibrations, respec-
tively. El-Sonbati et al. [29] observed similar C@N band at
1555 cmꢀ1, N@N band at 1540 cmꢀ1. Teimouri et al. observed sim-
ilar N@N band at 1502 cmꢀ1. The correlations of calculated vibra-
tional frequencies using B3LYP and B3PW91 methods with that
of experimental analogs are plotted in Fig. 8. The correlation be-
tween the calculated (B3LYP and B3PW91) and the experimental
frequencies were found to be linear, and the equations can be given

96
M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Table 7
Vibrational frequencies (cmꢀ1), their PED and assignments for HQD.
No.
m
(Exp.)
m
(Calc.)
PED⁄ (K > 10%)
Assignment
IR
Raman
B3PW91
B3LYP
1
2
3
4
5
6
7
8
3408
3163
3120
3092
3088
3079
3047
3041
3008
2995
2995
2958
2938
2877
2841
1726
1614
1592
1573
1561
1527
1503
1496
1475
1472
1468
1463
1455
1455
1439
1433
1416
1401
1381
1365
1360
1344
1301
1279
1275
1247
1235
1214
1199
1193
1184
1168
1155
1151
1146
1136
1126
1110
1071
1062
1030
996
3441
3163
3111
3110
3106
3103
3091
3087
3055
3043
3043
3002
3000
2926
2926
1768
1614
1597
1583
1573
1541
1506
1484
1479
1472
1466
1461
1450
1447
1446
1435
1419
1414
1386
1380
1372
1361
1317
1285
1280
1255
1244
1213
1206
1194
1182
1173
1161
1151
1141
1138
1136
1119
1066
1059
1039
1012
1010
978
3457
3216
3116
3113
3111
3106
3093
3087
3056
3042
3042
3003
3000
2931
2930
1756
1605
1586
1577
1562
1530
1498
1481
1475
1475
1470
1457
1455
1455
1445
1437
1425
1409
1387
1366
1364
1353
1296
1281
1264
1244
1234
1209
1198
1195
1185
1175
1163
1151
1142
1140
1135
1117
1067
1052
1039
1006
997
100 K(Oq–H)
99 K(Ob–H)
94 K(CbH)
96 K(CbH)
97 K(CqH)
99 K(CqH)
99 K(CqH)
93 K(CqH)
94 K(CqH)
98 K(CmH)
91 K(CmH)
98 K(CmH)
91 K(CmH)
95 K(CmH)
95 K(CmH)
85 K(C@O)
48 K(CqCq) + 10 H(CqCqH)
64 K(CbCb)
50 K(CqCq)
44 K(CqCq) + 18 K(CNq)
71 K(CbCb)
55 K(N@N) + 14 H(CqCqH)
47 H(HCmH)
38 H(HCmH) + 14 H(CbCbH)
87 H(CbCbH)
74 H(HCmH)
51 H(CcOH)
60 H(HCmH)
83 H(HCmH)
75 H(CcOH)
52 H(CqOH) + 10 H(HCmH)
64 H(HCmH)
41 H(NqCH) + 17 H(CqOH)
51 H(CqCqH)
44 K(CbCb) + 10 K(CqCq)
21 H(NqCH) + 14 H(CqOH)
33 K(CqNq) + 10 H(CqOH)
74 K(CbCb)
53 K(CqO) + 12 K(CqNq)
37 K(CbO) + 28 K(CbCb)
43 K(CqNa) + 12 H(CqCqH)
38 K(NaCb)
55 H(CqCqH) + 11 K(CCcO)
42 H(CbCbH) + 24 H(OCmH)
39 H(CbCbH) + 24 H(CqCqH)
24 H(CbCbH) + 24 H(CqCqH)
66 H(OCmH)
49 H(CqCqH) + 11 K(CqO)
15 H(OCmH) + 14 H(CbCbCb)
35 H(OCmH)
m
m
OqH
ObH
ms CbH
ma CbH
ms CqH
m
CqH
ma CqH
CqH
ma CqH
m
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
ma Cm
ma Cm
ma Cm
ma Cm
ms Cm
ms Cm
m
m
m
m
m
m
m
d HCm
d HCm
d CbCbH
d HCm
d CcOH
d HCm
d HCm
d CcOH
d CqOH
H
H
H
H
H
H
1741
1624
1592
1576
1567
1540
1505
1491
1488
1471
1469
1463
1458
1458
1440
1431
1420
1407
1379
1365
C@O
CqCq
CbCb
CqCq
CqCq
CbCb
N@N
H
H
H
H
H
d HCm
d NqCH
d CqCqH
H
m
CbCb
d NqCH + d CqOH
m
m
m
m
m
m
CqNq
CbCb
Cq–O
Cb–O +
CqNa
NaCb
1313
1284
1281
1258
1238
1226
1195
1190
1181
1171
1153
1150
1144
1138
1122
m
Cb–Cb
d CqCqH
d CbCbH +
d CbCbH + d CqCqH
d CqCqH + d CbCbH
q
CH3
q
CH3
d CqCqH
q
q
q
q
CH3 + d CbCbCb
CH3
CH3
CH3
78 H(OCmH)
26 H(OCmH) + 13 H(CqCqH)
38 H(CqCqH) + 13 K(CqCq)
37 H(CqNCq) + 11 H(CbCbH)
43 K(CcO) + 24 K(CcCb)
27 K(CqCq) + 25 H(CqCqH)
67 K(CqCq)
65 K(CmO)
32 K(CmO) + 30 K(NaCb)
79 T(CqCq)
90 T(CqCq)
79 T(CqNq)
84 T(CbCb)
39 T(CbCb) + 20 H(CNN)
50 T(CbCb) + 13 T(NN)
78 P(Cq)
d CqCqH
d CNC (ring q)
m
m
m
1074
CcO + m CcCb
CqCq + dCqCqH
CqCq (ring breathing q)
1021
1000
981
964
956
940
932
909
878
859
834
817
800
787
775
751
743
725
ma Cm–O
ms Cm–O + m NaCb
977
964
952
938
928
896
884
837
816
812
795
781
776
764
749
975
945
935
922
892
881
832
816
810
807
779
776
764
745
m
s
s
s
s
s
c
CqCq
CqCq
CqNq
CbCb
CbCb + d CNN
CbCb
Cq
886
38 H(CqCqN)
d CqCqNq
s
s
69 T(CqCq) + 12 T(CqN)
72 K(CcO) + 10 P(Cc)
82 H(CbCbCb)
50 P(Cq)
39 P(Cc) + 20 P(Cb)
44 P(Cc)
CqCq
CcO
789
759
d CbCbCb
c
c
c
Cq
Cc
Cc
+ c Cb

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
97
Table 7 (continued)
No.
m
(Exp.)
m
(Calc.)
PED⁄ (K > 10%)
Assignment
IR
Raman
713
B3PW91
B3LYP
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
712
707
684
663
647
642
632
621
606
581
556
520
511
486
472
460
432
416
408
400
380
363
334
306
300
260
252
228
208
187
174
164
142
132
123
115
101
80
728
718
700
689
662
659
638
631
609
600
561
537
508
480
475
464
450
417
411
403
379
367
323
293
287
266
250
241
204
174
172
155
148
143
139
129
114
83
728
717
699
675
664
659
639
634
611
602
563
538
510
483
478
466
453
420
412
402
381
369
323
294
289
268
251
241
204
175
174
156
148
145
142
130
113
86
22 P(Cb)
42 H(OCcH)
c Cb
d OCcO
d CqCqCq
687
668
646
34 H(CqCqCq) + 13 K(CqCq)
92 T(Cq–O)
58 H(CbCbN) + 13 H(CbCbO)
39 P(Cc) + 13 P(Cb)
60 H(CqCqNq)
s
CqO
d CbCbN + d CbCbO
Cc Cb
d CqCqNq
c
+ c
54 P(Cq)
63 P(Cq)
c
c
Cq
Cq
611
590
560
520
517
487
472
457
440
48 H(OCcO) + 12 H(CbCbCb)
39 H(CqCqO) + 20 H(CqCqCq)
17 H(CqCqN) + 15 H(CqNCq) + 14 H(CqCqCq)
15 P(Cb) + 15 H(CbOCm
64 H(CqCqCq)
d OCcO
d CqCqO + d CqCqCq
d (ring q)
)
c
(ring b)
d CqCqCq (ring q)
CqCq CqNq
d CbCbCb (ring b)
42 T(CqCq) + 30 T(CqNq)
50 H(CbCbCb)
s
+ s
25 T(CqCq) + 24 T(CbCb)
36 T(CqCq) + 35 T(CqNq)
37 H(CbCcO) + 23 H(CqCqO)
31 H(CbCcO) + 24 H(CqCqO)
24 T(CqCq) + 24 T(CqNa)
29 H(CbOCm)
23 T(CqCc) + 22 H(CbCbO)
44 H(CqCqOq) + 15 H(CqCqCq)
34 T(CbCb) + 19 T(CqOm
s
s
CqCq
CqCq
+
+
s
s
CbCb
CqNq
d CbCcO + d CqCqO
d CbCcO + d CqCqO
403
386
s
CqCq
d CbOCm
CqCc + d CbCbO
d CqCqOq (skeletal)
CbCb CqOm
+ s CqNa
s
98
99
)
s
+ s
38 H(CbOCb) + 33 H(CbCbO)
16 H(CbCbCc)
d CbOCb + d CbCbO
d CbCbCc
d CbCbCb (ring b)
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
30 H(CbCbCb) + 11 T(Cq–Na)
24 H(CbOCm) + 13 P(Cq)
40 P(Cb) + 26 T(CmO)
21 T(CqCq) + 17 P(Cq) + 13 T(CqCq)
51 T(CmO)
77 T(CqCq)
55 T(CmO)
43 H(CbCbCc) + 33 T(CmO)
16 H(NaCqCq) + 15 T(CmO)
34 T(CmO) + 34 P(Cq)
63 T(CbO)
63 T(CbCc)
66 T(CbO)
34 T(CbCb) + 33 P(Cb)
58 H(CNN)
27 T(Na–Na) + 20P(Cb) + 20T(CbCb)
78 T(CNa)
d CbOCm + c Cq
c
c
s
s
s
Cb
(ring q) butterfly vibration
Cm
CqCq
Cm
+ s CmO
O
O
d CbCbCc
d NaCqCq
+
+
c Cq
s
Cm
O
O
s
Cm
s
s
s
s
c
CmO +
CbO
CbCc
CbO
72
61
53
47
38
30
75
67
58
37
31
16
75
66
58
36
30
16
(ring b)
d CNN
s
s
(N@N)
CNa
Force constant contributions greater than 10% are included in Potential Energy Distributions, Subscript; q; quinoline ring,b; benzene ring, m; methyl group, c: carboxylic acid
group, s; symmetric, a; asymmetric vibrations. Vibrations:
m
; stretching, d; in-plane bending,
c; out-of-plane bending, s; torsional vibrations; q, rocking.
0.5
0.4
0.3
0.2
0.1
0.0
4000
3500
3000
2500
2000
1500
1000
500
B3LYP
B3PW91
y = 1.0121x - 3.6901
y = 1.0108x - 1.9195
R2 = 0.9998
R2 = 0.9998
0
0
500
1000
1500
2000
2500
3000
3500
200
300
400
500
600
700
Cal. Wavenumbers, cm-1
Wavelength (nm)
Fig. 8. Correlation graphics between experimental and calculated frequencies of
HQD.
Fig. 9. The UV–vis absorption spectrum of HQD.

98
M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
Table 8
Experimental and calculated visible absorption maxima and their corresponding oscillator strengths of HQD obtained by the methods CIS, TD and ZINDO.
Exp.
Calculated/kcal (nm), CIS
Calculated/kcal (nm), TD
Calculated/kcal (nm), ZINDO
Wavelength
Oscillator strength
Wavelength
Oscillator strength
Wavelength
Oscillator strength
527
309
229
368.50
335.11
245.28
0.4490
0.7792
0.0488
475.81
436.60
357.31
0.3402
0.6094
0.0103
553.13
506.93
347.43
0.2125
0.7678
0.1273
ln(h -E ) (eV)
ν
g
-2.4 -2.3 -2.2 -2.1
-2
-1.9 -1.8 -1.7 -1.6 -1.5
13
0.05
11
9
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
-0.35
-0.40
7
5
3
1
-1
-3
-5
-7
slope = 0.495
1.94
2.02
2.10
2.18
2.26
2.34
2.42
h
(eV)
ν
Fig. 10. Plots of d(ln(
a
h
m)/dln(h
m
) h
m
and ln(ahm) ln(hm ꢀ Eg).
scaled frequency values using the scale factors given above yielded
better results which are in a better agreement with experimental
frequencies. The %relative errors of the frequencies obtained after
scaling are 2.66% for B3LYP and 2.62% for B3PW91.
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
Optical properties of HQD
Indirect bandgapE = 1.90 eV
g
The optical properties of HQD were analyzed by UV–vis absorp-
tion spectroscopy. The UV–vis absorption spectrum was recorded
in ethanol solution. Fig. 9 shows the UV–vis optical absorption
spectrum of HQD that gave three maxima at the wavelengths of
229, 309, 527 nm at room temperature. The strongest peak was ob-
served at 527 nm in the visible region is associated with a band gap
of
229 and 309 nm and these may be ascribed to the excitation of
the -electrons which is localized on the quinoline ring.
p–
p⁄ electronic transition. Also, small peaks were observed at
Direct band gap E = 1.95 eV
g
p
0.1
The optical band gap of HQD, Eg, (ELUMO ꢀ EHOMO: energy differ-
ence between the levels of the lowest unoccupied and highest
occupied molecular orbital) can be determined from the absor-
bance spectrum according to the Tauc method [31–36]. This meth-
od assumes a parabolic variation of the absorption band edge with
photon energy. The optical band gap of HQD was estimated by fun-
damental relation given by [37–40]:
1.70 1.78 1.86 1.94 2.02 2.10 2.18 2.26 2.34
h
(eV)
ν
Fig. 11. Plots of (ahm) m for direct band gap and plots of (ahm) m
2 versus h 1/2 versus h
for indirect band gap of HQD.
as; y = 1.0121x ꢀ 3.6901, (R2 = 0.9998) and y = 1.0108x ꢀ 1.9195
(R2 = 0.9998) for B3LYP and B3PW91, respectively. It can be con-
cluded that the frequency values obtained with both methods are
satisfactorily explains experimental vibrational frequencies but the
method B3PW91 gives slightly better experimental frequencies
when compared with the values obtained by B3LYP calculations
as stated by Balachandran in his study [30]. The frequency values
calculated theoretically caused systematic errors at these levels
due to known assumptions of the method. For obtaining better fre-
quency values, the scaling factors were calculated to be 0.9669 and
0.9635 for the methods B3LYP and B3PW91, respectively. The
m
ð
a
h
m
Þ ¼ Bðh
a
m
ꢀ EgÞ
ð1Þ
where
is absorption coefficient, h
m
is photon energy, B is a propor-
tionality constant, the exponent m depends on the nature of the
transition, m = 1/2, 2, 3/2, or 3 for direct and non-direct allowed
and also forbidden direct, and forbidden non-direct transitions,
respectively. The curve of d(ln(
Fig. 10 was plotted by using Eq. (1). The curve of ln(
ln(h
ꢀ Eg) is plotted by using this value of Eg and the slope of this
curve m was found approximately a value of 0.5. The Eg was deter-
ah
m
)/dln(h
m
) versus h
m
as shown in
ahm
) versus
m
2
mined by extrapolating the linear part of (ahm) versus hm curve,

M. Saçmacı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 88–99
99
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and it was found to be 1.95 eV (Fig. 11). The indirect optical energy
band gap of HQD was also determined with a value of 1.90 eV by
extrapolating the linear portion of this plot in Fig. 11 for m = 2. This
azo dye has a direct energy band gap of 1.95 eV and the indirect
transition involves a defect energy band; these results can be attrib-
uted to the molecular structure of HQD.
The absorption maxima (kmax) of HQD were also calculated by
the methods of CIS, TD and ZINDO using ethanol as the solvent.
The experimental and theoretical visible absorption maxima of
HQD were given in Table 8. The closest value to the experimental
kmax observed at 527 nm was obtained with ZINDO method as
553 nm when compared with the other methods. The other peaks
at 309 and 229 nm measured experimentally are in a better agree-
ment with the calculated values of CIS.
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Conclusions
The experimental and theoretical investigations of HQD have
been performed successfully by using NMR, IR & Raman, UV–vis
and quantum chemical calculations. The computational investiga-
tion of this compound by DFT (B3LYP and B3PW91) methods is
consistent with all the experimentally measured spectroscopic val-
ues. HQD gives an absorption peak at about 527 nm in the visible
region, and is associated with an optical band gap. This means that
HQD is visible light sensitive, and can be also used as a visible re-
gion sensor besides its good dye property.
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The authors wish to thank to the Research Foundation of Bozok
University for the financial support for this study, to Mr. Mustafa
Akgül for checking grammatical errors, and to Prof. Dr. Zeki
Büyükmumcu for his valuable discussions. In this paper DFT calcu-
lations were performed at TUBITAK ULAKBIM, High Performance
and Grid Computing Center (TR-Grid e-Infrastructure).
_
_
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.05.068.
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