Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol

Article abstract of DOI:10.1016/j.saa.2014.02.186

A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C₁₅H₁₅N₁O₂, reveals that the structure is adopted to its E configuration about the azomethine CN double bond. The compound adopts a enol-imine tautomeric form with a strong intramolecular O-H?N hydrogen bond. The single crystal X-ray diffraction analysis at 296 K crystallizes in the monoclinic space group P21/c with a = 13.4791(11) ?, b = 6.8251(3) ?, c = 18.3561(15) ?, α = 90°, β = 129.296(5)°, γ = 90° and Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried out by FT-IR and UV-vis spectrometry. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the relocation of the electron density were determined. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties were also investigated. In addition, frontier molecular orbitals analysis have been performed from the optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S), have been investigated.

Full text of DOI:10.1016/j.saa.2014.02.186

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Experimental (X-ray, FT-IR and UV–vis spectra) and theoretical methods
(DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol
b
a
Zeynep Demirciog˘lu a, , Çig˘dem Albayrak , Orhan Büyükgüngör
⇑
a Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, TR-55139 Kurupelit-Samsun, Turkey
b Department of Chemistry, Faculty of Arts and Science, Sinop University, TR-57000 Sinop, 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
ꢀ
Experimental (X-ray, FT-IR and UV–
vis spectra) methods and theoretical
methods (DFT study) were
investigated.
ꢀ
ꢀ
Nonlinear optical properties (NLO)
and natural bond orbital (NBO)
analysis were analyzed.
Mulliken population method and
natural population analysis (NPA)
were calculated.
a r t i c l e i n f o
a b s t r a c t
Article history:
A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C15H15N1O2,
reveals that the structure is adopted to its E configuration about the azomethine C@N double bond.
The compound adopts a enol–imine tautomeric form with a strong intramolecular OAHꢁ ꢁ ꢁN hydrogen
bond. The single crystal X-ray diffraction analysis at 296 K crystallizes in the monoclinic space group
Received 11 December 2013
Received in revised form 24 February 2014
Accepted 25 February 2014
Available online 12 March 2014
P21/c with a = 13.4791(11) Å, b = 6.8251(3) Å, c = 18.3561(15) Å,
a = 90°, b = 129.296(5)°, c = 90° and
Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried
out by FT-IR and UV–vis spectrometry.
Keywords:
Schiff bases
Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/
B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge
delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO)
analysis.
Electronic structures were discussed by TD-DFT method and the relocation of the electron density were
determined. The energetic behavior of the title compound has been examined in solvent media using
polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population
method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties
were also investigated. In addition, frontier molecular orbitals analysis have been performed from the
Natural population analysis (NPA)
Density functional theory (DFT)
Molecular electrostatic potential (MEP)
Nonlinear optical properties (NLO)
Natural bond analysis (NBO)
optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (
potential ( ), electronegativity ( ), hardness ( ), and softness (S), have been investigated.
Ó 2014 Elsevier B.V. All rights reserved.
x), chemical
l
v
g
⇑
Corresponding author. Tel.: +90 362 312 1919.
E-mail address: zeynep.kelesoglu@omu.edu.tr (Z. Demirciog˘lu).
http://dx.doi.org/10.1016/j.saa.2014.02.186
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
749
Mo Ka radiation (k = 0.71073 Å) and the w-scan technique were
Introduction
used. The structure was solved by direct methods using SHELXS-
97 [15] and refined through the full-matrix least-squares method
using SHELXL-97 [16], implemented in the WinGX [17] program
suite. Non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All H atoms were located in a difference Fourier
map and were refined isotropically. Data collection: Stoe X-AREA
[17], cell refinement: Stoe X-AREA [17], data reduction: Stoe XRED
[18]. The general-purpose crystallographic tool PLATON [19] and
ORTEP-3 [17] was used for the structure analysis and presentation
of the results. The structure was refined to Rint = 0.030 with 2132
Schiff bases are important in diverse fields of chemistry and bio-
chemistry owing to their biological activity [1,2] and can be classi-
fied according to their photochromic or thermochromic properties
[3,4]. From observations on some thermochromic and photochro-
mic Schiff base compounds, it was proposed that molecules exhib-
iting thermochromism are planar, while those exhibiting
photochromism are non-planar [5,6]. o-hydroxy schiff base ligands
are of interest mainly because of the existence of typical hydrogen
bonds and tautomerism between the OAHꢁ ꢁ ꢁN in phenol-imine
and NAHꢁ ꢁ ꢁO in keto-amine forms and N+AHꢁ ꢁ ꢁOꢂ in zwitterionic
forms [7–9]. This compound undergoes tautomerism by proton
transfer between the hydroxy O atom and the imine N atom,
namely the enol–imine tautomer. In Schiff base compounds, the
imine nitrogen can act as an inter- or intramolecular hydrogen-
bond acceptor and the hydroxyl oxygen in salicylaldehyde deriva-
tives can act as an intermolecular hydrogen-bond acceptor. Schiff
bases non-linear properties have an importance for the design of
various molecular electronic devices such as optical switches and
optical data storage devices [10,11].
observed reflections using I > 2r(I) threshold. Details of the data
collection conditions and the parameters of the refinement process
are given in Table 1.
Computational details
The entire calculations conducted in the present work were per-
formed at B3LYP levels included in the Gaussian 03 W package [20]
program together with 6-31G(d,p) basis set function of the density
functional theory (DFT) utilizing gradient geometry optimization
[21]. Initial geometry generated from standard geometrical param-
eters was minimized without any constraint in the potential energy
surface at Hartree–Fock level, adopting the standard 6-31G(d,p) ba-
sis set. We have utilized the gradient corrected density functional
theory [22] with three parameter hybrid functional (B3) [23] for
the exchange part and the Lee–Yang–Parr (LYP) correlation function
[24], accepted as a cost effective approach for the computation of
molecular structure, vibrational frequencies and energies of opti-
mized structures. By combining the results of the Gaussview pro-
gram [25] with symmetry considerations, vibrational frequency
assignments were made with a high degree of accuracy.
The significant values for energy, bond lenghts, bond angles and
torsions were obtained by using B3LYP/6-31G(d,p) basis set. The
optimized structural parameters were used in the vibrational fre-
quency calculations at the DFT levels to characterize all stationary
points as minima. At the optimized structure of the examined spe-
cies, no imaginary frequency modes were obtained proving that a
true minimum on the potential energy surface was found. We have
scaled the vibration frequency numbers with standard scaling fac-
tor 0.9627 to neglect of vibrational anharmonicity.
For Schiff bases, NLO studies provide the key functions of fre-
quency shifting, optical modulation, optical switching, optical lo-
gic, and optical memory for the emerging technologies in areas
such as telecommunications, signal processing, and optical
interconnections.
The title molecule was determined by single crystal X-ray dif-
fraction technique. In the present study, it is planned to have a
joint experimental and theoretical investigation of FT-IR and
UV–vis spectra. Electronic absorption spectra of the title com-
pound were predicted by using time-dependent density functional
theory (TD-DFT) [12–14] in the calculation of electronic excitation
energies for gas and solution phases (different solvent media). The
excitation energies, wavelengths and oscillator strengths were ob-
tained at TD-DFT level at the optimized geometry. In addition to, it
is also planned to illuminate theoretical determination of the opti-
mized molecular geometries, HOMO–LUMO energy gap, MEP, NLO,
Mulliken charges, NPA and NBO analysis of the title compound by
using density functional theory (DFT) with B3LYP/6-31G(d,p) basis
set. In addition, the ionization potential, electron affinity, electro-
philicity index, chemical potential, electronegativity, hardness
and softness are determined.
Experimental and computational methods
Table 1
Crystal data and structure refinement parameters for the title compound.
Synthesis
Chemical formula
C15H15N1O2
Color/shape
Formula weight
Temperature
Crystal system
Space group
Unit cell parameters
Orange/plate
241.28
296 K
Monoclinic
P21/c
a = 13.4791(11) Å
b = 6.8251(3) Å
c = 18.3561(15) Å
For the preparation of (E)-3-methoxy-2-[(p-tolylimino)
methyl]phenol compound the mixture of 2-hydroxy-6-methoxy-
benzaldehyde (0.5 g, 3.3 mmol) in ethanol (20 ml) and 4-methy-
laniline (0.35 g, 3.3 mmol) in ethanol (20 ml) was stirred for 2 h
under reflux. The crystals suitable for X-ray analysis were obtained
from ethanol by slow evaporation (yield;%84, m.p.; 342–344 K).
a
= 90°
b = 129.296(5)°
Instrumentation
c
= 90°
Volume
Z
Density
1306.85(16) Å3
4
The FT-IR spectrum of the title compound was recorded in the
4000–400 cmꢂ1 region with a Bruker Vertex 80V FT-IR spectrome-
ter using KBr pellets. Absorbtion spectra were determined on Uni-
cam UV–vis spectrometer.
1.226 Mgmꢂ3
0.086 mmꢂ1
STOE IPDS 2/v-scan
2.83–26.50°
14,753
Absorption coefficient
Diffractometer/meas. meth.
h range for data collection
Unique reflections measured
Total reflection/observed reflections
Goodness of fit on F2
2704/2132
1.15
Crystal structure determination
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.165, wR1 = 0.155
R2 = 0.058, wR2 = 0.073
The single-crystal X-ray data were collected on a STOE IPDS II
image plate diffractometer at 296 K. Graphite-monochromated

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Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
Frontier molecular orbital (FMO) analysis have been used to
Results and discussion
clarify the information regarding charge transfer within the mole-
cule. HOMO–LUMO energy gap provides important information
about stability of the structure. Besides, energy gap has a major
role in non-linear optic materials.
Crystal structure and optimized geometry
The optimized molecular structure of the schiff base with atom
numbering scheme adopted in this study is shown in Scheme 1.
The molecule have the space group P21/c, with four molecules
per unit cell (Z = 4). From single crystal X-ray diffraction data, it
is found that the crystal belongs to mononclinic which have the
following dimensions; a = 13.4791(11) Å, b = 6.8251(3) Å,
c = 18.3561(15) Å and the angle of b = 129.296(5)°.
The tautomerism appears in o-hydroxy Schiff bases as a result
of intramolecular proton transfer from oxygen atom to nitrogen
atom. This proton transfer resulted in two tautomeric structures
as enol and keto forms in the solid state. These tautomeric forms
are related to two types of intramolecular hydrogen bonds as
OAHꢁ ꢁ ꢁN in enol form and NAHꢁ ꢁ ꢁO in keto form and N+AHꢁ ꢁ ꢁOꢂ
in zwitterionic forms. In our study of title compound is inclined
to enol form because of the strong O1AH1ꢁ ꢁ ꢁN1 intramolecular
hydrogen bonding (Fig. 1, Table 2).
The theoretical electronic absorption spectra have been calcu-
lated by using TD-DFT method. The values of excitation energies,
oscillation strengths (f), wavelengths (k) and energy gaps of the
molecule have been calculated for gas phase and different solu-
tions. Since solvent effects play an important role in absorption
spectrum of the compound, in this paper, the integral equation for-
malism polarizable continuum model (PCM) [26,27] dealing with
solvent effect was chosen in excitation energy calculations. Sol-
vents with different polarities, dielectric constants and protic–
aprotic properties have affected the values of total energy, excita-
tion energy, EHOMO, ELUMO and dipol moment. Frontier molecular
orbital (FMO) energies, energy gap (
to increase with increasing polarity of the solvent. Different sol-
vents ( = 78.39, water; = 46.7, DMSO; = 24.3, ethanol; = 4.9,
chloroform; = 2.3, benzene) at the B3LYP/6-31G(d,p) were carried
DE) and dipole moment tends
e
e
e
e
e
out by using the PCM method.
A significant intramolecular interaction (O1AH1ꢁ ꢁ ꢁN1) is noted
involving phenol atom O1 and nitrogen atom N1 and constitutes a
six-membered ring S(6) [29]. The study compound has no intermo-
lecular hydrogen bonding. The weak van der Waals interactions is
also effective in crystal packing. The single bond futures of the
C1AN1 (1.420(2) Å), C8AC9 (1.445(2) Å), C14AO1 (1.341(2) Å),
and strong double bond character of the C8@N1 (1.279(2) Å) are
showing that this bond lengths are confirmed enol-imine tauto-
meric form. This characteristic bond lenghts are in harmony with
previous works [30,31].
The natural bonding orbitals (NBO) calculations were per-
formed using NBO program [28] under Gaussian 03 W [30] pack-
age at the DFT/B3LYP/6-31G(d,p) level. NBO calculations interpret
various second order interactions between the filled orbitals of
one subsystem and vacant orbitals of another subsystem, which
is a measure of the intramolecular delocalization or hyper conjuga-
tion. The redistribution of electron density in various bonding,
antibonding orbitals and E(2) (energy difference between donor
and acceptor natural bond orbitals) energies have been calculated
by natural bond orbital (NBO) analysis to give clear evidence of sta-
bilization originating from the hyperconjugation of various intra-
molecular interactions.
X-ray results show the dihedral angle between the planes of
two aromatic rings is 23.16(6)° and in optimized geometry it is
Molecular electrostatic potential analysis (MEP) has been used
to find the reactive sites of the compound. The electrostatic poten-
tial contour map with the negative regions (assigned to red) of MEP
are related to electrophilic attacks and positive regions (assigned to
blue) are related to nucleophilic reactivity. In addition, the net
charges are calculated with Mulliken population method and nat-
ural population method (NPA). The calculated natural atomic
charges values were obtained from NBO analysis.
OH
CH3
N
OCH3
Scheme 1. Chemical diagram of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol.
Fig. 1. Ortep 3 diagram for (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, with the atom numbering scheme. Dashed lines are show the O1AH1ꢁ ꢁ ꢁN1 intra molecular
hydrogen bonds.

Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
751
Table 2
Hydrogen bonding geometry for the title compound.
DAHꢁꢁꢁA
DAH
HꢁꢁꢁA
DꢁꢁꢁA
DAHꢁꢁꢁA
O1AH1ꢁꢁꢁN1
0.9(3)
1.76(3)
2.59(2)
154(3)
33.84°. The nearly planar of the planes show the thermochromic
properties. In addition, the dihedral angle between the nearly pla-
nar S(6) ring with C1AC6 and C9AC14 aromatic rings are
23.54(24)° and 0.38(5)°, respectively.
Fig. 2. Superimposition of the X-ray structure (red) and calculated structure (black)
of the title molecule. (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
The optimized (theoretical) geometry parameters were calcu-
lated by B3LYP/6-31G(d,p). The selected bond lengths, bond angles
and torsion angles for the optimized structure and X-ray geometry
of the molecule are listed in Table 3. As expected, the results show
a little difference in experimental and computational processes.
The difference observed between the experimental and theoretical
parameters are due to the ignored effects. These effects are the
molecular interactions which the theoretical methods cannot take
into account. While the experimental results belong to the solid
state, the calculated results belong to the isolated gaseous phase.
Namely, the optimized geometry with B3LYP is preferred more
planar conformation than X-ray geometry. The structural discrep-
ancies between the optimized molecule and crystallographically
observed geometry can be analyzed quantitatively by root mean
square (r.m.s.) overlay. The r.m.s. fit of the atomic positions of
experimental and calculated geometries is 0.152 Å, indicating the
agreement between the two geometries (Fig. 2).
Vibrational spectra
Fig. 3. Experimental (red) and theoretical DFT/B3LYP/631G(d,p) (black) FT-IR
spectrum of the title compound. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
Experimental and calculated FT-IR spectrum of the title com-
pound was given in Fig. 3 and vibration frequencies of compound
are compared in Table 4. The vibrational frequencies obtained by
quantum chemical calculation are typically larger than their exper-
imental counterparts, and thus, empirical scaling factors are usu-
ally used to match the experimental vibrational frequencies [32].
The computational studies on vibrational frequencies were
performed at B3LYP/6-31G(d,p) level. In order to improve the
agreement between the calculated and the experimentally ob-
served values, the calculated harmonic frequencies have been scale
down via introduction of scaling factor. The vibrational frequencies
were scaled by 0.9627 [33]. The frequencies obtained by theoreti-
cal method is in accordance with the observed FT-IR spectrum.
Theoretical and experimental FT-IR spectrum of the title molecule
was given in Fig. 3.
Depending on X-ray and IR results, the title compound shows
enol form rather than keto form. In the spectrum, there are two
important absorption bands to characterize the title compound.
One of these appears at 2000–3000 cmꢂ1 region. It is attributed
Table 3
Selected molecular structure parameter for the title compound.
Bond lengths (Å), bond angles (°) and
torsions (°)
Experimental DFT/6-
31G(d,p)
C1AC2
C4AC7
1.37(2)
1.51(3)
1.403
1.35
to the
t(O1AH1) stretching vibration peak which broaden due to
N1AC1
1.42(2)
1.40
the formation of strong intramolecular O1AH1ꢁ ꢁ ꢁN1 hydrogen
N1AC8
1.27(2)
1.29
bond in the structure. The
t(O1AH1) band is observed at
C8AC9
1.44(2)
1.44
2931.8 cmꢂ1 in theoretical of FT-IR result. These stretching mode
which was also supported by the literature. The result obtained
from X-ray diffraction study, indicates that C8@N1 is the double
O1AC14
1.48(4)
1.51
O1AH1
0.90(2)
1.00
C10AO2
1.36(2)
1.36
O2AC15
1.41(2)
1.42
bond character. As
1615.16 cmꢂ1 corresponds to
other characteristic IR absorption band at 3023.76–2975.86 cmꢂ1
corresponds to (CAH) stretching vibrations of aromatic benzene
rings. The agreement between calculation results and experimen-
tal results are very good. The (@CAH) rocking vibrations of aro-
matic structures generally occur in the region 1370–1350 cmꢂ1
The absorption band at 1365 cmꢂ1 corresponds to
(C8AH8) rock-
a
result of this, absorption band at
C7AC4AC3
C7AC4AC5
C1AN1AC8
N1AC8AC9
C14AO1AH1
C9AC8AH8
C10AO2AC15
C2AC1AN1
C8AH8AN1
C8AC9AC10
C9AC8AN1AC1
C2AC1AN1AC8
C8AC9AC10AC11
C11AC10AO2AC15
C9AC10AO2AC15
N1AC1AC2AC3
121.6(2)
121.0(2)
120.42(14)
121.98(15)
104.9(16)
119.0
118.56(14)
117.63(15)
119.0
120.02(15)
ꢂ178.47(16)
153.98(18)
ꢂ178.83(17)
1.6(3)
121.01
121.20
121.19
121.63
107.03
116.95
118.57
117.87
121.40
120.48
177.29
149.03
ꢂ179.98
0.375
t
(C8@N1) stretching vibration. The
t
c
.
c
ing vibrations of the title compound. In addition, the experimental
IR results show the aromatic b(CAH) out-of-plane bending vibra-
tions appear in 815.76–753.47 cmꢂ1 frequency. The rocking vibra-
tions of
c(C7AH3) group are generally observed in the region
1070–1010 cmꢂ1 [34]. This mode appears at 1017.65 cmꢂ1 and
1024.7 cmꢂ1 in experimental and theoretical FT-IR spectrum,
ꢂ179.54 (18) ꢂ179.74
ꢂ177.93(18) ꢂ179.90

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Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
Table 4
The HOMO and LUMO energy calculated by B3LYP/6-31G(d,p)
method as shown below:
Comparison of the experimental and calculated vibrational frequencies (cmꢂ1).
Experimental
IR with KBr
DFT/
Assignmentsa
B3LYP/
631-
G(d,p)
HOMO energy (B3LYP) = ꢂ5.57 eV
LUMO energy (B3LYP) = ꢂ1.49 eV
HOMO–LUMO energy gap (B3LYP) = 4.08 eV
3023.76
–
3068.36
3056.35
3101.74
3115.46
3078.44
3083.31
3006.5
2978.5
3005.5
2973.7
2922.2
2931.8
2910.77
1462
t
(CAH) R2 +
(CAH) R1
t(CAH) R1
This electronic absorption corresponds to the transition from
the ground to the first excited state and is mainly described by
one electron excitation from the highest occupied molecular orbi-
tal (HOMO) to the lowest unoccupied molecular orbital (LUMO).
The calculations indicate that the title compound have 66 occupied
molecular orbitals. Fig. 4 shows the surfaces of HOMO and LUMO
and their energies. The HOMO–LUMO energy gap explains the
eventual charge transfer interactions taking place within the mol-
ecule and it is also can be supported with NLO results, as we de-
scribe later. The ionization energy (I) and electron affinity (A) can
be obtained as, I = ꢂEHOMO and A = ꢂELUMO. Mulliken electronega-
c
3023
2975
a
(C7AH3)
2900–3000
2944.56
2844.90
2000–3000
2900
1463.41
1567.79
1597.79
c
t
(N1@C8AH8)
(O2AC15AH3)
t(O1AH1)
a
(O2AC15AH3)
1567.14
1595.19
1618.2
1567.14
1489.29
1506.6
1558.6
1455.6
1429.6
1345.85
1243.8
t
(N@CAC) + (CAC)R1,R2 + c(CAH)R2
t
tivity (
a property of molecule that measures the extent of chemical reac-
tivity. It is the reciprocal of hardness S = 1/2 . It is defined as the
reciprocal of hardness ( ) and
= (I ꢂ A)/2 [19]. The electrophilic-
ity index ( ), ) is a measure of energy lowering due
= (ꢂ
2/2
v) can be calculated as follows: v = (I + A)/2. Softness (S) is
1615.16
1493.98
1567.79
c
t
(N@C)
(CAC)R1,R2 +
g
c(CAH)R1,R2 + c(C15AH3)
g
g
x
x
v
g
1463.41
1441.15
1365.74
1228.45
1294.02
1186.25
1095.24
1017.64
877.5
t
c
c
t
(CAC)R2 +
(C15AH3)
(C8AH8)
c(CAH)R2 + c(O1AH1) + w(N@CAC)
to maximal electron flow between donor and acceptor. The values
of electronegativity, chemical hardness, softness, and electrophilic-
ity index are 3.05 eV, 2.04 eV, 0.24 eV, ꢂ3.05 eV in gas phase,
respectively for the title molecule. A large HOMO–LUMO gap im-
plies high stability. High stability of a molecule reflects its low
reactivity toward chemical reactions in some sense. Considering
the chemical hardness, large HOMO–LUMO gap means a hard mol-
ecule and small HOMO–LUMO gap means a soft molecule. We can
assume that the stability of the molecule to softness with least
HOMO–LUMO gap. In addition, soft molecules has an easily chan-
ged electron distribution so it is corresponding to more reactive
site than hard molecules.
(O2AC15) +
c(CAH)R2
1177.38
1093.79
1024.7
860.48
862.36
800.9
t
t
c
c
(CAN) + (CAH)R1,R2
(O2AC15) + b(CAH)R1,R2
(C7AH3)
(O1AH1)
c
841.62
815.76
781.65
b(CAH)R1 + b(CAH)R2
753.47
a
m, stretching;
c, rocking; a, scissoring, x, wagging; b, bending. Abbreviations:
R1, C1AC6; R2, C9AC14 phenyl ring.
TD-DFT at B3LYP/6-31G(d,p) level by adding polarizable contin-
uum model (PCM) calculations were started from gas phase and
solution phase optimized geometry using same level of theory.
As a result of theoretical calculation, excitation energies, oscillation
strengths (f), wavelengths (k), energy gaps (EHOMO–ELUMO) and total
energies were obtained successfully.
respectively. The other vibrational frequencies can be seen in
Table 4, particularly.
The UV–vis spectra of the title compound in various organic sol-
vents (ethanol, DMSO, benzene and chloroform) were recorded
within 200–800 nm range (Fig. 5). The characteristic experimental
UV–vis absorption bands of the molecule in ethanol, DMSO, chloro-
form and benzene are comparatively given in Table 5. It is observed
for all solvents that there are absorption bands less than 400 nm.
The theoretical UV–vis spectrum of the title compound in several
solvents (benzene, chloroform, ethanol, DMSO and water) has been
studied. We give priority to these solvents because of chloroform
and benzene is a nonpolar solvent, DMSO is a polar aprotic solvent.
Besides, ethanol is a polar protic solvent acting as both hydrogen
Frontier molecular orbitals (FMOs) and UV–vis absorption spectra
The FMOs (frontier molecular orbitals) are important in deter-
mining such properties as molecular reactivity and the ability of
a molecule to absorb light. These FMOs is very important for opti-
cal and electric properties [35]. Both the highest occupied molecu-
lar orbitals (HOMOs) and lowest unoccupied molecular orbitals
(LUMOs) are the main orbitals taking part in chemical stability.
The HOMO represents the ability to donate an electron, LUMO as
an electron acceptor representing the ability to obtain an electron.
Fig. 4. Molecular orbital surfaces and energies for the HOMO and LUMO of the title compound.

Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
753
As well, FMOs are the most important orbitals because they
play important roles in chemical reactions. The energy gap ( E)
D
is important to influence the stability of a molecule and determines
the chemical reactivity, kinetic stability, polarizability and chemi-
cal activity of a molecule [38]. If the molecule have a large energy
gap, they are more stable molecule as a chemical activity. As a
known, hard molecules have large energy gap and soft molecules
have small energy gap. So, softs are more polaritable and more
chemical reactive regions than hard molecules [39]. With respect
to results, title compound is more polarizable, more reactive and
more soft molecule as related compounds [40,41].
Molecular electrostatic potential
Molecular electrostatic potential (MEP) is related to the elec-
tronic density and is a very useful descriptor in understanding sites
for electrophilic attack and nucleophilic reactions as well as hydro-
gen bonding interactions [42,43]. The electrostatic potential V(r) is
also well suited for analyzing processes based on the ‘‘recognition’’
of one molecule by another, as in drug-receptor, and enzyme sub-
strate interactions, because it is through their potentials that the
two species first ‘‘see’’ each other. For the systems studied the
MEP values were calculated as described previously, using the
Eq. (1) [44]:
Fig. 5. The solvent effect on UV–vis spectra of the title compound in DMSO, ethanol,
chloroform and benzene.
donor and acceptor and water is not a dissolvent for the title com-
pound. The greater the dielectric constant, the greater the polarity.
These solvents cover a wide range of polarities and they have dif-
ferent dielectric constants (benzene
e
= 2.3; chloroform
= 78.39).
e = 4.9;
EtOH = 24.3; DMSO = 46.7 and Water e
e
e
In the UV–vis spectra of o-hydroxy schiff base compounds, the
presence of an absorption band at less than 400 nm indicates the
enol imine tautomeric form. On the other hand, compounds adopt
keto-amine tautomeric form show a new absorption band at great-
er than 400 nm [36,37]. It is clear from our results that there is no
absorption band observed at greater than 400 nm region in any
solvent for the title compound. This station is supported that the
molecule adopts the enol form rather than keto form. As can be
seen in Table 5, the experimental wavelengths are lower than
400 nm and in the theoretical UV–vis spectrum of the title mole-
cule absorption bands occur at 341.07 nm, 344.19 nm,
343.04 nm, 341.64 nm, 343 nm and 341.07 nm for gas phase, ben-
zene, chloroform, ethanol, DMSO and water, respectively. The re-
sults of our analysis support that the compound show enol form
rather than keto form, obviously.
Z
X
ZA
jRA ꢂ rj
q
ðr0Þ
VðrÞ ¼
ꢂ
dr0
ð1Þ
jr0 ꢂ rj
where the summation runs over all the nuclei A in the molecule and
polarization and reorganization effects are neglected. ZA is the
charge of the nucleus A, located at RA and q
(r0) is the electron den-
sity function of the molecule. Experimental V(r) computed with
electron densities obtained from X-ray diffraction data has been
used to explore the electrophilicity of hydrogen bonding functional
groups. In the majority of the MEPs, while the maximum positive
region which preffered site for nucleophilic attract indications as
blue color, the maximum negative region which preffered site for
electrophilic attract indications as red color. The different values
of the electrostatic potential at the surface are represented by dif-
ferent colors. Potential increases in the order red < orange < yel-
low < green < blue. The color code of these maps is in the range
between ꢂ0.0462 a.u. (deepest red) and 0.0462 a.u. (deepest blue)
in compound, where blue shows the strongest attraction and red
shows the strongest repulsion. Regions of negative V(r) is usually
associated with the lone pair of electronegative atoms. The study
of experimental and theoretical V(r) shows that H-donor and
H-acceptor properties of molecules are revealed by positive and
negative regions, respectively, so that the formation of a H-bond
can be regarded as the consequence of a complementarity between
the electrostatic potentials [45]. According to MEP map analysis re-
sults, the negative regions of whole molecule is localed on oxygen
atoms (red coded region) and the positive regions (blue encoded re-
gions) of whole molecule is localed on the methyl group attached to
In the evaluation of the results was based on the oscillator
strengths (f) which greater than 0.4. It is well known that
p ?
pꢃ
transition is shifted to long wavelength with increasing the solvent
polarity. The reason of this shifting, the dipole moment of solvent
is produced dipole moment over the solute matter. The frontier
molecular orbitals were mainly localized over the whole molecule
except for methyl groups and
the molecule. Then, we can say that the electronic transitions are
mainly derived from the contribution of bands
pꢃ transition.
p ?
pꢃ interactions were common in
p
?
The total energy, energy gap, dipole moment, and oscillator
strength increase with the increasing polarity of the solvent.
Charge delocalization of the molecule increases with the increasing
polarity of solvent, therefore, induces the dipol moments raised.
However, excitation energies (wavelengths) were not changed lin-
early with increasing polarity. Forwhy, deviations from linearity is
likely related to chemical properties for solvents.
Table 5
Calculated energies, excitation energies, oscillator strengths, dipole moments and frontier orbital energies for the title compound.
Gas phase (
e
= 1)
Benzene (
e
= 2.3)
Chloroform (
e
= 4.9)
Ethanol (
e
= 24.3)
DMSO (
e
= 46.7)
Water (e = 78.39)
ETOTAL (a.u.)
EHOMO (eV)
ELUMO (eV)
ꢂ785.8516
ꢂ5.57
ꢂ1.49
4.08
341.07
0.5086
3.4166
–
ꢂ785.8571
ꢂ5.7021
ꢂ1.5725
4.1295
344.19
0.5236
3.8973
304
ꢂ785.8599
ꢂ5.7443
ꢂ785.8620
ꢂ785.8622
ꢂ5.7813
ꢂ1.649826
4.1320
343
0.5821
4.4129
296
ꢂ785.8630
ꢂ5.7742
ꢂ1.6403
4.1339
341.07
0.4965
4.4678
–
ꢂ5.7753
ꢂ1.64356
4.1317
341.64
0.4965
4.3951
235
ꢂ1.613091
4.1312
343.04
0.5278
4.1705
298
D
E (eV)
Excitation energy (nm)
Oscillator strength (f)
l
(D)
Experimental wavelength (nm)

754
Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
Table 6
Calculated net charges by Mulliken population method and natural population
analysis (NPA).
Atom B3LYP/6-31G (d,p) Mulliken
charges
B3LYP/6-31G (d,p) (NPA) natural
charges
C1
C2
C3
C4
C5
C6
C7
C8
0.24
ꢂ0.03
ꢂ0.09
0.08
ꢂ0.09
ꢂ0.05
ꢂ0.34
0.24
0.13
ꢂ0.22
ꢂ0.22
ꢂ0.03
ꢂ0.22
ꢂ0.25
ꢂ0.69
0.12
C9
ꢂ0.02
ꢂ0.23
C10
C11
C12
C13
C14
C15
N1
O1
O2
H1
0.29
0.36
ꢂ0.09
ꢂ0.04
ꢂ0.04
0.25
ꢂ0.04
ꢂ0.6
ꢂ0.52
ꢂ0.55
0.31
ꢂ0.36
ꢂ0.18
ꢂ0.31
0.40
ꢂ0.32
ꢂ0.52
ꢂ0.69
ꢂ0.52
0.51
Fig. 6. Molecular electrostatic potential map calculated at B3LYP/6-31G(d,p).
the carbonyl group and concentrated on the hydrogen atoms
around.
H2
0.05
0.24
As a shown in Fig. 6, there are several possible sites for electro-
philic attacks over the O1, O2 and N1 atoms. The maximum nega-
tive electrostatic potential is substantially over the O1 atom
because of the strong intramolecular hydrogen bond. As can be
seen from the MEP map of the title molecule, while regions having
the negative potential are over the electronegative atoms, the re-
gions having the positive potential are over the hydrogen atoms.
Red and blue regions in the MEP map refer to the regions of neg-
ative and positive potentials and correspond to the electron rich
and electron-poor regions, respectively, whereas the green color
signifies the neutral electrostatic potential. The MEP surface pro-
vides necessary information about the reactive sites.
H3
H5
H6
0.04
0.03
0.05
0.12
0.12
0.10
0.07
0.04
0.05
0.05
0.11
0.11
0.23
0.23
0.24
0.24
0.24
0.24
0.22
0.24
0.24
0.25
0.20
0.20
H7A
H7B
H7C
H8
H11
H12
H13
H15A
H15B
H15C
0.11
0.23
Mulliken population analysis and natural populatin analysis
Natural bond orbital (NBO) analysis
The calculation of effective atomic charges plays a dominant
role in the application of quantum mechanical calculations to
molecular systems. The Mulliken analysis is the most common
population analysis method. This calculation which depicts the
charges of the every atom in the molecule distribution of positive
and negative charges are vital to increase or decrease of bond
length between the atoms. The survey of literature reveals that
effective atomic calculations gave an important role in the applica-
tion of chemical calculation to molecular system because of atomic
charges effect dipole moment, molecular polarizablity, electronic
structure, acidity–basicity behavior and a lot of properties of
molecular system [46]. In addition, it also has been used to de-
scribe the electrostatic potential surfaces [47–49]. The total atomic
charge values are obtained by Mulliken population analysis and
natural charges are obtained by NBO (natural bond analysis) [50]
are listed in Table 6. The two methods predict the same tendencies.
As can be seen in Table 6, all the hydrogen atoms have a net posi-
tive charge. The obtained atomic charge shows that the H1 atom
has bigger positive atomic charge (0.31 e; 0.51 e) than the other
hydrogen atoms. N1, O1 and O2 atoms are most negative atomic
charges (ꢂ0.61 e; ꢂ0.52 e), (ꢂ0.52 e; ꢂ0.69 e), (ꢂ0.55 e; ꢂ0.52 e).
According to these results, NBO’s net charges are slightly longer
than Mulliken charges. The intention is to accurately model partial
charge magnitude and location within a molecule. Mulliken popu-
lation analysis is a good way to account for differences in electro-
negativities of atoms within the molecule and frequently uses for
supporting the MEP contour map. MEP and Mullikan population
method can be use for interpreting and predicting the reactive
behavior of a wide variety of chemical systems in both electro-
philic and nucleophilic reactions.
Natural bond orbital analysis provide an efficient method for
studying intra and inter molecular bonding and interaction among
bonds, and provides a convenient basis for investigating charge
transfer or conjugative interaction in molecular systems [51]. The
bonding–anti bonding interaction can be quantitatively described
in terms of the NBO approach that is expressed by means of sec-
ond-order perturbation interaction energy E(2) [52–55]. This en-
ergy represents the estimate of the off-diagonal NBO Fock matrix
element. The stabilization energy E(2) associated with
i(donor) ? j(acceptor) delocalisation is estimated from the sec-
ond-order perturbation approach as given below:
F2ði; jÞ
Eð2Þ ¼ q
ð2Þ
i ej
ꢂ
ei
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments (orbital energies) and F(i, j) is the off-diagonal Fock matrix
element. The larger the E(2) value, the more intensive is the interac-
tion between electron donors and electron acceptors, i.e. the more
donating tendency from electron donors to electron acceptors and
the greater the extent of conjugation of the whole system. DFT/
B3LYP/6-31G (d,p) level computation is used to investigate the var-
ious second-order interactions between the filled orbitals of one
subsystem and vacant orbitals of another subsystem, which is a
measure of the delocalization or hyper-conjugation. Delocalization
of electron density between occupied Lewis type (bond or long pair)
NBO orbitals and formally unoccupied (antibonding and Rydgberg)
non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor
interaction.

Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
755
In this paper, natural bond orbital method [56] at B3LYP/6-
31G(d,p) level of theory using NBO program [57] under Gaussian
2003 program package. By natural bond orbital (NBO) method,
the effect of substitution on the hydrogen bond strength, the
charge distributions, steric effects, and electron delocalization
can be also investigated. In our study, we have investigated the
intramolecular interaction, rehybridization and electron delocal-
ization within the molecule. The corresponding results have been
tabulated in Table 7.
NBOs are localized electron pair orbitals for bonding pairs and
lone pairs. The hybridization of the atoms and the weight of each
atom in each localized electron pair bond is calculated in the ide-
alized Lewis structure. A normal Lewis structure would not leave
any antibonding orbitals, so the presence of antibonding orbitals
shows deviations from normal Lewis structures. Antibonding local-
ized orbitals are called non-Lewis NBOs. If the occupancy is not 2.0,
then there are deviations from an ideal Lewis structure (Table 7). In
order to study the small deviations from idealized Lewis structure,
the donor–acceptor interaction approach is adopted. Strong elec-
tron delocalization in best Lewis structure will also show up as do-
nor–acceptor interactions. Our calculation has done by examining
all possible interactions between ‘filled’ (donor) Lewis-type NBOs
and ‘empty’ (acceptor) non-Lewis NBOs. Since these interactions
lead to loss of occupancy from the localized NBOs of the idealized
Lewis structure into the empty non-Lewis orbitals, they are re-
ferred to as ‘delocalization’ corrections to the natural Lewis struc-
ture. As a result of our study, the structure is a type of Lewis
structure with% 97.06; valance-non Lewis with% 2.77 and Rydberg
non-Lewis with% 0.16.
As an be seen from results, the
-electron delocalization is involved due to the
whereas, the hyperconjugative interactions due to the various
types of orbital overlaps such as
However, only
pꢃ and n ? pꢃ interactions are also possible ac-
p
-conjugation/resonance due to
p
p ?
pꢃ interactions
p
? , ? , p ? , p ? .
pꢃ pꢃ pꢃ pꢃ pꢃ
p
?
cording to experimental results.
The intramolecular hyperconjugative interactions are formed by
the orbital overlap between
p
(CAC) and pꢃ(CAC) bond orbitals
which result in intramolecular charge transfer causing stabilization
of the system. These interactions are observed as an increase in
electron density (occupacy) in (CAC) anti bonding orbitals that
weakens the respective bonds [58]. The occupancy at
p bonds for
(CAC) benzene ring is (ꢄ1.63–1.70) and pꢃ bonds for (CAC) benzene
ring is (ꢄ0.31–0.39) clearly indicates strong delocalization leading
to stabilization of energy in the range of 11.15–23.56 kcal/mol. In
Table 7
Significant donor–acceptor interactions of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol and their second order perturbation energies calculated at B3LYP level using 6-31G
(d,p) basis set.
a
Donor(i) (occupancy)
Type
EDA,% EDB,%
Acceptor (j) (occupancy)
Type
–
EDA,% EDB,%
–
E(2) (kcal/mol)
Ej ꢂ Eib (a.u.)
1.98
F(i, j)c (a.u.)
BD C1AC2
(1.97392)
BD C1AC2
(1.97392)
BD C1AC2
(1.97392)
BD C1AC2
(1.97392)
BD C1AC2
(1.97392)
BD C2AC3
(1.68664)
BD C2AC3
(1.68664)
BD C1AC6
(1.63850)
BD C1AC6
(1.63850)
BD C1AN1
(1.98351)
BD C1AN1
(1.98351)
BD C1AN1
(1.98351)
BD C4AC5
(1.64608)
BD C4AC7
(1.98423)
BD C8AC9
(1.97429)
BD C8AC9
(1.97429)
BD C8AC9
(1.97429)
BD C8AN1
(1.98708)
BD C8AN1
(1.98708)
BD C8AN1
(1.91160)
BD C9AC10
(1.96813)
BD C9AC10
(1.96813)
r
50.85
49.15
50.85
49.15
50.85
49.15
50.85
49.15
50.85
49.15
49.79
50.21
49.79
50.21
49.60
50.40
49.60
50.40
40.02
59.98
40.02
59.98
40.02
59.98
49.39
50.61
50.71
49.29
48.48
51.52
48.48
51.52
48.48
51.52
39.90
60.10
39.90
60.10
37.54
62.46
50.80
49.20
50.80
49.20
RY ꢃ C3
0.74
0.034
(0.00470)
r
r
r
r
p
p
p
p
r
r
r
p
r
r
r
r
r
r
p
r
r
BD ꢃ C1AC6
rꢃ
rꢃ
rꢃ
rꢃ
pꢃ
pꢃ
pꢃ
pꢃ
rꢃ
rꢃ
rꢃ
pꢃ
rꢃ
rꢃ
rꢃ
rꢃ
pꢃ
A
49.48
50.52
59.98
40.02
50
3.37
1.24
2.46
2.33
19.73
19.93
20.28
18.67
3.14
1.60
1.25
1.14
1.28
1.28
0.28
0.29
0.29
0.29
1.28
1.37
1.21
0.28
1.20
1.13
1.28
1.21
1.31
2.20
0.36
1.10
0.97
0.058
0.034
0.050
0.049
0.068
0.068
0.068
0.066
0.057
0.042
0.023
0.068
0.043
0.062
0.043
0.051
0.044
0.061
0.062
0.054
0.048
(0.02963)
BD ꢃ C1AN1
(0.02830)
BD ꢃ C2AC3
(0.01283)
50
BD ꢃ C8AN1
(0.01156)
60.10
39.90
50.40
49.60
50.61
49.39
50.61
49.39
50.21
49.79
51.52
48.48
60.10
39.90
20.35
79.65
50.40
49.60
49.46
50.54
59.98
40.02
60.10
39.90
48.55
51.45
20.35
79.65
–
BD ꢃ C1AC6
(0.39055)
BD ꢃ C4AC5
(0.34993)
BD ꢃ C4AC5
(0.34993)
BD ꢃ C2AC3
(0.31653)
BD ꢃ C8AC9
(0.02466)
BD ꢃ C8AN1
(0.01156)
BD ꢃ O1AH1
0.52
(0.08761)
BD ꢃ C1AC6
(0.39055)
20.90
1.97
4.20
BD ꢃ C4AC5
(0.02249)
BD ꢃ C1AN1
(0.02830)
BD ꢃ C8AN1
1.80
(0.01156)
BD ꢃ C9AC14
(0.03440)
2.66
1.76
2.09
BD ꢃ O1AH1
(0.08761)
RY ꢃ C9
(0.00635)
BD ꢃ C1AC6
pꢃ
rꢃ
rꢃ
50.40
49.60
66.13
33.87
68.38
31.62
11.15
3.24
2.92
(0.39055)
BD ꢃ C14AO1
(0.01760)
BD ꢃ C15AO2
(0.00828)
(continued on next page)

756
Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
Table 7 (continued)
a
Donor(i) (occupancy)
Type
EDA,% EDB,%
Acceptor (j) (occupancy)
Type
EDA,% EDB,%
E(2) (kcal/mol)
Ej ꢂ Eib (a.u.)
1.26
F(i, j)c (a.u.)
BD C9AC10
(1.96813)
BD C9AC14
(1.97360)
BD C10AC11
(1.70357)
BD C10AC11
(1.70357)
BD C10AO2
(1.99133)
BD C12AC13
(1.71811)
BD C12AC13
(1.71811)
BD C13AC14
(1.97794)
BD C13AC14
(1.97794)
BD C13AC14
(1.97794)
BD C13AC14
(1.97794)
BD C14AO1
(1.99442)
BD C15AO2
(1.99286)
BD C15AO2
(1.99286)
BD O1AH1
(1.98471)
LP C9
r
50.80
49.20
51.45
48.55
43.53
56.47
43.53
56.47
32.37
67.63
45.46
54.54
45.46
54.54
49.45
50.55
49.45
50.55
49.45
50.55
49.45
50.55
33.87
66.13
31.62
68.38
31.62
68.38
79.65
20.35
–
BD ꢃ C10AC11
(0.02486)
rꢃ
49.54
50.46
67.63
32.37
–
3.39
0.058
r
p
p
r
p
p
BD ꢃ C10AO2
rꢃ
–
3.10
32.19
23.56
1.07
1.05
0.15
0.30
1.48
0.14
0.27
0.051
0.081
0.075
0.036
0.096
0.056
(0.02782)
LP C9
(1.14923)
BD ꢃ C12AC13
pꢃ
rꢃ
–
54.54
45.46
49.56
50.44
–
(0.31907)
BD ꢃ C11AC12
(0.01495)
LP ꢃ C14
57.05
13.81
(0.90741)
BD ꢃ C10AC11
pꢃ
56.47
43.53
(0.38199)
RY ꢃ C12
r
r
r
(0.00483)
–
–
–
–
0.66
1.60
1.98
1.40
0.032
0.042
RY ꢃ C12
(0.00297)
RY ꢃ O1
–
–
0.66
1.95
1.94
1.13
1.45
1.83
1.37
1.29
0.13
0.14
0.15
0.79
0.032
0.043
0.032
0.040
0.056
0.075
0.103
0.108
0.099
0.153
(0.00152)
BD ꢃ O1AH1
rꢃ
rꢃ
–
20.35
79.65
49.20
50.80
–
r
r
(0.08761)
BD ꢃ C9AC10
(0.02677)
1.53
r
r
r
–
–
–
–
RY ꢃ C10
1.10
(0.00746)
BD ꢃ C9AC10
rꢃ
rꢃ
pꢃ
pꢃ
pꢃ
rꢃ
49.20
50.80
50.55
49.45
62.46
37.54
56.47
43.53
54.54
45.46
20.35
79.65
2.81
(0.02677)
BD ꢃ C13AC14
(0.02409)
5.51
BD ꢃ C8AN1
70.56
79.57
50.85
36.01
(1.14923)
LP C9
(1.14923)
LP C14
(0.90741)
LP N1
(1.84249)
(0.21779)
–
–
–
BD ꢃ C10AC11
(0.38199)
BD ꢃ C12AC13
(0.31907)
BD ꢃ O1AH1
(0.08761)
a
E(2) means energy of hyperconjucative interactions (stabilization energy).
Energy difference between donor (i) and acceptor (j) NBO orbitals.
b
this paper, n ? pꢃ interactions are due to the carbon lone pair elec-
tron donation from n(C9) atom to (anti bonding acceptor) pꢃ(-
C8@N1) and pꢃ(C10AC11) show the strongest stabilization to the
system by 70.56 kcal/mol and 79.57 kcal/mol, respectively. Besides,
this interactions are strengthens the intramolecular O1AH1ꢁ ꢁ ꢁN1
hydrogen bond. The most important interaction energy (the most
strongest energy) is related to the resonance in the title molecule
and it is electron donating from lone pair (n) and anti bonding unoc-
cupied non-Lewis NBO orbital. The strong stabilization denotes the
nonlinear optical (NLO) properties are currently attracting consid-
erable attention because of their potential applications in optoelec-
tronic devices of telecommunications, information storage, optical
switching, and signal processing. Comparing with organic mole-
cules, metal complexes can offer great scope for the creation of
multifunctional NLO materials. Recently, various multidimensional
NLO metal complexes have emerged as candidates for second-or-
der NLO materials because of their potential advantages over
one-dimensional chromophores, such as increasing b responses
without undesirable losses of transparency in the visible region,
possessed better phase-matching because of their larger off-diago-
nal components [59].
larger delocalization. According to our calculations, all
r ?
rꢃ inter-
actions demonstrate the weak E(2) values in the range of 1.07–
4.20 kcal/mol. The delocalization of electron density (occupancy)
between occupied Lewis type
r
(CAC) and
r
(CAN) bonds and unoc-
The output from GAUSSIAN03W provides 10 components of the
3 ꢅ 3 ꢅ 3 matrix as bxxx; bxxy; bxyy; byyy; bxxz; bxyz; byyz; bxzz;
byzz; bzzz; respectively, from which the x; y and z components of
b are calculated as described earlier [60]. When reporting a single
value of b; one of the common formats is to simply treat the three
independent values for b as a quasi Pythagorean problem and solve
for the average b by the following equation:
cupied antibonding Rydgberg non-Lewis orbitals correspond to
weak hyperconjugative interactions. In this paper, we observed
r
?
rꢃ interactions only in theoretical computations and these
are correspond to lower E(2) values. The experimental results show
pꢃ and n ? pꢃ interactions, clearly. In Table 7, the% valence
pꢃ
?
hybrids are also shown. In addition, hyperconjugative interactions
are associated with% ED (occupacy). In order to determine the ideal
Lewis type, we should check out% valence hybrids of the atoms and
the weight of each atom in each localized electron pair bond.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
btop
¼
b2x þ b2y þ b2z
ð3Þ
, the average linear polarizability
The total static dipole moment
l
a,
Nonlinear optical effects (NLO)
and the first hyperpolarizability b can be calculated by using Eqs.
(4)–(6), respectively.
Molecule-based second-order nonlinear optical (NLO) materials
have recently attracted much interest because they involve new
scientific phenomena and because they offer potential applications
in emerging optoelectronic technologies. Molecular materials with
ꢀ
ꢁ
2
l
¼
lx2
þ
ly2
þ
lz2
ð4Þ

Z. Demirciog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 748–758
757
phase were performed. Computational and experimental UV–vis
studies for various organic solvents of different polarities indicate
that the stability of the molecule increases upon an increase in
the polarity of solvent. Molecular orbital coefficient analyses sug-
Table 8
Calculated dipole moments (
components for the title compound.
l
), polarizability (
a
) and first hyperpolarizability (b)
bxxx = ꢂ628.51 a.u.
bxxy = 118.33 a.u.
bxyy = 12.364 a.u.
byyy = ꢂ25.61 a.u.
bxxz = 80.76 a.u.
lx = ꢂ0.18 a.u.
gest that the electronic spectrum corresponds to strong
transitions. The results show that molecule exists enol form even
in solvent media. The movement of -electron cloud from donor
p ?
pꢃ
l
l
l
y = 1.32 a.u.
z = 0.09 a.u.
tot = 1.33 Debye
p
a
a
a
a
a
a
a
xx = 330.36a.u.
xy = 6.37 a.u.
yy = 178.90 a.u.
xz = 4.34 a.u.
yz = ꢂ10.84 a.u.
zz = 81.20 a.u.
tot = 29.16 Å3
to acceptor i.e. intramolecular charge transfer can make the mole-
cule more polarized and the low HOMO–LUMO energy gap could
be responsible for the non-linear optical properties of the mole-
cule. The title compound exhibited good NLO property and it was
approximately 14.5 times greater than urea. We can conclude that
the title molecule is an attractive object for future studies of non-
linear optical properties. Natural bond orbital (NBO) calculations
reveals the delocalization or hyper-conjugation interaction, intra-
molecular charge transfer and stabilization energy of molecule.
According to NBO results, we can determine the ideal Lewis type
structure. We hope the results of this study will help researchers
to analyze and synthesize new materials.
bxyz = ꢂ16.50 a.u.
byyz = ꢂ9.18 a.u.
bxzz = 7.44 a.u.
byzz = 15.06 a.u.
bzzz = 7.64 a.u.
btot = 5.432 ꢅ 10ꢂ30 cmꢂ5/esu
À
Á
1
3
2
a ¼ axx
þ
ayy
þ
azz
ð5Þ
h
i
1=2
2
2
2
btot ¼ ðbxxx þbxyy þbxzzÞ þðbyyy þbyzz þbyxxÞ þðbzzz þbzxx þbzyy
Þ
ð6Þ
Supplementary data
The dipole moment, polarizability and the first hyperpolarizability
were calculated using polar = ENONLY at the level of B3LYP/6-
31G(d,p) and the results obtained from calculation. The calculated
CCDC 965353 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, by emailing data_re-
quest@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
polarizability
a and first hyperpolarizability b of title compound
are 29.16 Å3 and 5.432 ꢅ 10ꢂ30 cm5/esu and the title molecule is
14.5 times greater than those of urea (a and b of urea of
3.8312 Å3 and 0.37289 ꢅ 10ꢂ30 cm5/esu), respectively [61].
The polar properties of the title molecule were calculated at the
B3LYP/6-31G(d,p) level using the Gaussian 03 W program package.
Acknowledgement
The calculated values of electronic dipole moment,
l, polarizabil-
The authors wish to acknowledge the Faculty of Arts and Sci-
ences, Ondokuz Mayis University, Turkey, for the use of the STOE
IPDS 2 diffractometer (purchased under Grant F.279 of the Univer-
sity Research Fund).
ity, , and the first hyperpolarizability, b for the title compound
a
are, 1.33 Debye, 29.16 Å3, 5.43 ꢅ 10ꢂ30 cmꢂ5/esu, respectively
(Table 8). It is well known that the substituents influence the
polarity of the molecules. The energy gap between HOMO and
LUMO of the title compound is 4.08 eV for gas phase. These small
HOMO–LUMO energy gap for the title compound indicate that
molecular charge transfer occur in the compound. Energy gap is
small and it is easy to notice that they can be sensitive to the influ-
ence of the polar environment. Determination of the energy gap,
the dipole moment and first order hyperpolarizability shows that
the title molecule is an attractive object for future studies of
non-linear optical properties.
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