Experimental and computational studies on zwitterionic (E)-1-((4- phenoxyphenyliminio)methyl)naphthalen-2-olate

Article abstract of DOI:10.1016/j.molstruc.2011.04.042

The Schiff base compound (E)-1-((4-phenoxyphenyliminio)methyl)naphthalen-2- olate has been synthesized and characterized by IR, UV-Vis, and X-ray single-crystal determination. Molecular geometry of the title compound in the ground state have been calculat

Full text of DOI:10.1016/j.molstruc.2011.04.042

Journal of Molecular Structure 997 (2011) 70–77
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Experimental and computational studies on zwitterionic
(E)-1-((4-phenoxyphenyliminio)methyl)naphthalen-2-olate
b
a
a
Gökhan Alpaslan a, , Mustafa Macit , Ahmet Erdönmez , Orhan Büyükgüngör
⇑
a Department of Physics, Faculty of Arts & Science, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
b Department of Chemistry, Faculty of Arts & Science, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The Schiff base compound (E)-1-((4-phenoxyphenyliminio)methyl)naphthalen-2-olate has been synthe-
sized and characterized by IR, UV–Vis, and X-ray single-crystal determination.
Received 1 March 2011
Received in revised form 27 April 2011
Accepted 27 April 2011
Available online 5 May 2011
Molecular geometry of the title compound in the ground state have been calculated using the density
functional method (DFT) with 6-31G(d,p) basis set and compared with the experimental data. The calcu-
lated results show that the optimized geometry can well reproduce the crystal structure. By using TD-DFT
method, electronic absorption spectra of the title compound have been predicted and a good agreement
with the TD-DFT method and the experimental ones is determined. Molecular orbital coefficient analyses
reveal that the electronic transitions are mainly assigned to n ? p⁄ and p ? p⁄ electronic transitions. To
investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d,p) level were performed
for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable
than NH form. In addition, molecular electrostatic potential and non-linear optical properties of the title
compound were performed at B3LYP/6-31G(d,p) level of theory.
Keywords:
Schiff base
Zwitterionic
DFT
MEP
Non-linear optical
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
and theoretical methods has been of great interest. Functional
material design, theoretical modeling of drug design and so on,
Schiff bases compounds have received special attention due to
their interesting termochromism and/or photochromism [1,2], bio-
logical properties [3,4], as well as a variety of potential applica-
tions, e.g. for optical data storage [1,2,5], as nonlinear optical
materials [6,7], anticorrosive materials [8] or anticancer medicines
[9–11]. Tautomerism and isomerism phenomena for these com-
pounds are of particular chemical and theoretical interest in the
context of their photochromic and thermochromic properties
has become possible as results of the development of the compu-
tational techniques. Many important properties such as molecular
orbitals, electrostatic potentials, dipole moment, non-linear optical
properties, vibrational frequencies can be predicted by various
computational techniques [20–22].
In this work, we present results of a detailed investigation of the
synthesis and structural characterization of (E)-1-((4-phenoxyphe-
nyliminio)methyl)naphthalen-2-olate (Scheme 2) using IR, UV–Vis
and single-crystal X-ray diffraction. The geometric parameters of
the title compound in the ground state were calculated using the
DFT/B3LYP/6-31G(d,p) method. The properties of the structural
geometry, molecular electrostatic potential (MEP) and non-linear
optical properties for the title compound at B3LYP/6-31G(d,p) level
were studied.
[2,12]. Photo- and thermo-chromism due to a change in the p-elec-
tron configuration induced by proton transfer [13,14] Such proton
exchanging materials can be utilized for the design of various
molecular electronic devices [15]. In general, Schiff bases display
two possible tautomeric forms, the phenol-imine (OH) and the
keto-amine (NH) forms. Depending on the tautomers, two types
of intramolecular hydrogen bonds are observed in Schiff bases:
O–Hꢀ ꢀ ꢀN in phenol-imine [16,17] and N–Hꢀ ꢀ ꢀO in keto–amine
[18,19] tautomers (Scheme 1). Another form of Schiff base com-
pounds is their zwitterionic tautomer, which is rarely seen for hy-
droxy derivatives. The characteristic property of this form is the
presence of ionic N+–Hꢀ ꢀ ꢀOꢁ hydrogen bond [12]. Investigation of
structural stability of compounds by both experimental techniques
2. Experimental and computational method
2.1. Synthesis
The compound (E)-1-((4-phenoxyphenylimino)methyl)naph-
thalen-2-olate was prepared by reflux a mixture of a solution con-
taining 2-hydroxy-1-naphthaldehyde (17.2 mg; 0.1 mmol) in
⇑
30 ml ethanol and
(18.5 mg, 0.1 mmol) in 20 ethanol. The reaction mixture was
a solution containing 4-phenoxyaniline
Corresponding author. Tel.: +90 3623121919.
E-mail address: gokhana@omu.edu.tr (G. Alpaslan).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.04.042

G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
71
Scheme 1. Tautomeric forms of o-hydroxy Schiff bases.
the DFT calculations with a hybrid functional B3LYP (Becke’s three
parameter hybrid functional using the LYP correlation functional)
at 6-31G(d,p) basis set by using Berny method [26,27] were per-
formed with the Gaussian 03 W software package [28] and Gauss-
view visualization program [29]. In order to investigate the solvent
effect on the calculated geometric parameters, we also carried out
optimization calculations in the three solvent (chloroform, ethanol
and water) at the B3LYP/6-31G(d,p) level using Polarizable Contin-
uum Model (PCM) method [30–33]. The electronic absorption
spectra were calculated using the time-dependent density func-
tional theory (TD-DFT) method [34–37]. Also, it is calculated in
ethanol solution using the PCM method. To investigate the tauto-
meric stability, some properties such as total energy, HOMO and
LUMO energies, and the chemical hardness [38] for the OH and
NH forms of the title compound were obtained at B3LYP/6-
31G(d,p) level in gas phase. These properties were also examined
for the title compound in solvent media with three kinds of solvent
(chloroform, ethanol, and water) using the PCM method. To inves-
tigate the reactive sites of the title compound the molecular elec-
trostatic potential was evaluated using the B3LYP/6-31G(d,p)
method. The linear polarizability and first hyperpolarizability
properties of the title compound were obtained from molecular
polarizabilities based on theoretical calculations.
Scheme 2. (E)-1-((4-phenoxyphenylimino)methyl)naphthalen-2-olate (C23H17
NO2).
-
stirred for two hours under reflux. The crystals of (E)-1-((4-phen-
oxyphenylimino)methyl)naphthalen-2-olate for X-ray analysis
were obtained from ethanol solution by slow evaporation (yield
72%; m.p. 382–384 K).
2.2. Instrumentation
The FT-IR spectrum of the title compound was recorded in the
4000–400 cmꢁ1 region with a Shimadzu FTIR-8900 spectropho-
tometer using KBr pellet. Electronic absorption spectrum was mea-
sured on a Unicam UV–VIS spectrophotometer in EtOH solvent.
2.3. X-ray crystallography
3. Results and discussion
A thin rod crystal of the compound with dimensions of
0.78 ꢂ 0.31 ꢂ 0.05 mm was mounted on goniometer and data col-
lection was performed on a STOE IPDS II diffractometer by the w
3.1. Description of the crystal structure
scan technique using graphite monochromated Mo K
a radiation
The title compound crystallizes in the monoclinic, C2/c space
group with Z = 8 in the unit cell. Fig. 1 shows Ortep-3 diagram of
the title compound with atom numbering scheme. The asymmetric
unit in the crystal structure contains only one molecule. The C11–
N1 [1.300(4) Å] and C2–O1 [1.304(4) Å] bonds of the title com-
pound are the most important indicators of the tautomeric type.
While the C2–O1 bond is of a double bond for the keto–amine tau-
tomer, this bond displays single bond character in phenol–imine
tautomer. In addition, the C11–N1 bond is also a double bond in
phenol–imine tautomer and of single bond length in keto–amine
tautomer [39,40]. However, these bond distances have intermedi-
ate values between single and double C–O (1.362 and 1.222 Å,
respectively) and C–N (1.339 and 1.279 Å, respectively) bond dis-
tance [41]. The shortened C2–O1 bond and the slightly longer
C11–N1 bond provide structural evidence for the zwitterionic tau-
tomeric form of the title compound. Besides, zwitterionic forms of
Schiff bases have an intramolecular ionic hydrogen bond (N+–
Hꢀ ꢀ ꢀOꢁ), and their N+–H bond lengths are longer than those ob-
served in neutral N–H bond lengths (0.87 Å) [42,43]. The N+–H
(k = 0.71073 Å) at 296 K. The systematic absences and intensity
symmetries indicated the monoclinic C2/c space group. A total of
13617 reflection (3586 unique) with [1.6o < h < 27.2°] were col-
lected in the w scan mode and cell parameters were determined
by using X-AREA software [23]. Absorption correction
(l
= 0.08 mmꢁ1) was obtained by the integration method via X-
RED32 software [23]. The crystal structure was solved by direct
methods using SHELXS-97 [24]. The maximum peaks and deepest
hole observed in the final
D
q
map were 0.12 and ꢁ0.12 e Åꢁ3
,
respectively. The scattering factors were taken from SHELXL-97
[24]. The molecular graphics were done using Ortep-3 for Windows
[25]. The data collection conditions and parameters of refinement
process are listed in Table 1.
2.4. Computational procedures
The molecular geometry is directly taken from the X-ray diffrac-
tion experimental results without any constraints. In the next step,

72
G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
Table 1
tain two intermolecular C–Hꢀ ꢀ ꢀ
p interactions (Fig. 2). The details
of C–Hꢀ ꢀ ꢀ interactions are given in Table 2.
Crystallographic data for the title compound.
p
Crystal data
Chemical formula
Crystal shape/color
Formula weight
Crystal system
Space group
C23H17NO2
Thin rod/yellow
339.38
Monoclinic
C2/c
a = 22.7537(19) Å
b = 5.7798(4) Å
c = 30.674(3) Å
b = 120.869(6)o
3462.5(5) Å3
8
3.2. Theoretical structure
The molecular structure of the title compound in the ground
state (in vacuo) is optimized by B3LYP methods with the
6-31G(d,p) basis set. The calculated results are listed in Table 3.
When the X-ray structure of the title compound is compared with
its optimized counterpart (see Fig. 3), conformational discrepan-
cies are observed between them. The dihedral angles between A,
B and C planes are calculated at 11.20° (A/B), 77.62° (A/C), 67.98°
(B/C) for B3LYP. The orientation of the three rings is defined
by the torsion angles C1–C11–N1–C12 [ꢁ179.3(3)°], C16–C15–
N2–C18 [ꢁ41.7(5)°] and C14–C15–N2–C18 [141.5(4)°], which have
been calculated as 178.4°, ꢁ34.6° and 149.5° for B3LYP/6-31G(d,p)
level.
As seen from Table 3, most of the calculated bond lengths and
the bond angles are slightly different from the experimental ones.
We noted that the experimental results belong to the solid phase
and theoretical calculations belong to the gas phase. In the solid
state the experimental results are related to molecular packing,
but in the gas phase the isolated molecules are considered in the
theoretical calculations. The maximum difference between the
experimental values and those obtained from the theoretical calcu-
lations is 0.043 Å for bond distances and 3.5° for bond angles.
A logical method for globally comparing the structure obtained
with the theoretical calculation is by superimposing the molecular
skeleton with that obtained from X-ray diffraction, giving a RMSE
of 0.0231 Å for B3LYP/6-31G(d,p) (Fig. 3).
Unit cell parameters
Volume
Z
Dx (Mg cmꢁ3
)
1.302
0.08
1424
0.78 ꢂ 0.31 ꢂ 0.05
l
(mmꢁ1
)
F000
Crystal size (mm3)
Data collection
Diffractometer/meas. meth
Absorption correction
Tmin
STOE IPDS II/w-scan
Integration
0.965
0.997
13617, 3586, 1239
Tmax
No. of measured, independent and observed
reflections
Criterion for observed reflections
Rint
I > 2r(I)
0.139
26.5
hmax
Refinement
Refinement on
F2
R[F2 > 2
r
(F2)], wR, S
0.062, 0.106, 0.89
3586
239
No. of reflection
No. of parameters
Weighting scheme
2
w ¼ 1=½r2ðF20Þ þ ð0:0843PÞ ꢃ
P ¼ ðF20 þ 2F2c Þ=3
0.12, ꢁ0.12
qmax, D )
qmin (e Åꢁ3
In addition, in order to evaluate the solvent effect to the geo-
metric parameters of the title compound, we carried out calcula-
tions in three kinds of solvent (water, ethanol, and chloroform)
with the B3LYP/6-31G(d,p) level using the PCM model and the re-
sults are given in Table 3. When the experimental and theoretical
structures are globally compared the obtained RMSE’s are
0.0251 Å for chloroform, 0.0263 Å for ethanol and 0.0244 Å for
water, respectively. According to these results, it may be concluded
that the B3LYP calculation well reproduce the geometry of the title
compound.
D
bond distance [1.16(5) Å] is comparable with that of zwitterions in
the literature [42–44].
The dihedral angles between the naphthalene plane A (C1–C10),
the benzene plane B (C12–C17) and the other benzene plane C
(C18–C23) are 7.54° (A/B), 86.47° (A/C) and 84.63° (B/C). It is also
known that Schiff bases may exhibit photochromism depending
on the planarity or non-planarity, respectively [45].
The molecular structure is stabilized by N1+–H1ꢀ ꢀ ꢀO1ꢁ intramo-
lecular hydrogen bond which generates an S(6) ring motif (Fig. 1)
[46]. The sum of the Van der Waals radius of the N and O atoms
[3.07 Å] is significantly longer than the intramolecular N1ꢀ ꢀ ꢀO1
[2.526(4) Å] hydrogen bond length [47]. The compound also con-
3.3. IR spectroscopy
The FT-IR spectrum of the title compound was given in Fig. 4.
The some characteristic bands of the stretching vibrations of the
Fig. 1. Ortep-3 diagram of the title compound. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. The
intramolecular hydrogen bond is shown as a dashed line.

G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
73
Table 3
Table 2
Selected molecular structure parameters.
Hydrogen-bond geometry (Å, °).
Parameters
Experimental B3LYP PCM
Chloroform Ethanol Water
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
1.46(5)
2.80
Dꢀ ꢀ ꢀA
2.526(4)
3.713(5)
3.956(5)
D–Hꢀ ꢀ ꢀA
150(3)
166
N1–H1ꢀ ꢀ ꢀO1
1.16(5)
0.93
0.93
C3–H3ꢀ ꢀ ꢀCg4i
C19–H19ꢀ ꢀ ꢀCg3ii
Bond lengths (Å)
C1–C11
C1–C2
C2–O1
C3–C4
C11–N1
C12–C17
C12–N1
C15–O2
C18–O2
C19–C20
C20–C21
Max. Dif.
RMSE
3.08
157
1.412 (4)
1.424(4)
1.304(4)
1.352(5)
1.300(4)
1.387(4)
1.396(4)
1.395(4)
1.387(4)
1.390(5)
1.353(5)
1.394
1.465
1.261
1.355
1.336
1.403
1.403
1.378
1.384
1.394
1.396
0.043
0.022
1.398
1.462
1.267
1.357
1.334
1.403
1.405
1.379
1.387
1.395
1.397
0.044
0.021
1.401
1.460
1.270
1.357
1.333
1.403
1.407
1.380
1.388
1.396
1.397
0.044
0.021
1.401
1.459
1.271
1.358
1.334
1.403
1.408
1.381
1.388
1.396
1.397
0.044
0.021
Symmetry code (i): x + 1/2, y + 1/2, z; (ii): x, y + 1, z.
(Cg3 and Cg4 are the centroids of the C12–C17 and C18–C23 rings, respectively).
NH, CH, CN and CO groups were observed. The IR spectrum of the
title compound shows band at 3420 cmꢁ1 due to N–H stretching
vibration. The weak bands in the range 3033–3000 cmꢁ1 corre-
spond to the symmetric and asymmetric stretching vibrations of
aromatic CH bonds. The characteristic region of 1600–1700 cmꢁ1
can be used to identify the proton transfer of Schiff bases. The title
compound shows a strong band at 1620 cmꢁ1 which is assigned to
C@N stretching vibration. Another characteristic region of the
Schiff bases derivate spectrum is 1100–1400 cmꢁ1, which is attrib-
uted to C–O stretching vibrations. The C–O stretching vibration
was observed at 1240 cmꢁ1 which confirms the presence of pheno-
late group in the compound.
Bond angles (°)
C11–C1–C2
C2–C1–C10
C11–N1–C12
C18–O2–C15
C14–C15–O2
C19–C18–O2
C23–C18–O2
N1–C11–C1
C21–C20–C19
Max. dif.
117.6 (4)
120.1 (4)
126.5 (4)
117.2 (3)
117.5 (4)
118.4 (4)
120.2 (4)
123.9 (3)
120.6 (4)
118.7
120.0
125.4
120.9
118.6
116.0
123.3
126.4
120.5
3.7
118.3
120.3
128.0
120.7
116.5
116.8
122.2
123.1
120.4
3.5
118.5
120.2
128.1
120.7
116.5
116.7
122.1
123.0
120.3
3.5
118.7
120.1
128.3
120.5
116.5
116.8
122.0
123.0
120.3
3.3
The presence of N–H, C–O and C@N stretching vibrations
strongly suggest that the title compound has zwitterionic form in
the solid state.
RMSE
1.4
1.1
1.23
1.1
Torsion angles (°)
C1–C11–N1–C12
3.4. Electronic absorption spectra
ꢁ179.3 (3)
177.4
178.7
178.6
ꢁ35.1
179.9
0.5
178.5
ꢁ35.8
179.8
0.9
C16–C15–O2–C18 ꢁ41.7 (5)
ꢁ64.9 ꢁ34.6
The UV–Vis electronic absorption spectrum of the title com-
pound was recorded within 200–600-nm range on a Unicam UV–
Vis spectrophotometer in EtOH solvent. The observed spectra
N1–C12–C17–C16 ꢁ179.6 (3)
179.2
3.0
179.9
0.6
138.6
C11–C1–C2–O1
ꢁ1.0 (5)
C19–C18–O2–C15 121.5 (4)
155.4
138.3
138
showed three bands at 442 nm (log
e = 3.889), 320 nm (log
e
= 3.657) and 264 nm (log = 3.878). The maximum absorption
e
Fig. 2. Packing diagram of the title compound.

74
G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
Fig. 3. Atom-by-atom superimposition of the calculated structure (red) over the
X-ray structure (blue) for the title compound.
wavelength at 442 nm can be assigned to n ? p⁄ transition indicat-
ing the NH form of the title compound. The other bands may be
due to p ? p⁄ transitions of the naphthalene and benzene rings.
These values are similar to those found in related compound
[48,49]. The electronic absorption spectra of 2-hydroxy Schiff bases
which exist mainly as phenol–imine structure indicate the pres-
ence of a band at <400 nm, whereas compounds that existing in
the keto–amine form show a new band, especially in polar and
nonpolar solvents at >400 nm [50–53]. According to these results,
the NH form is dominant in ethanol solvent which has absorption
band at 442 nm (Fig. 5).
Electronic absorption spectra of the title compound were calcu-
lated by using TD-DFT method based on the B3LYP/6-31G(d,p) le-
vel optimized structure in gas phase. The TD-DFT theoretical
absorption band calculations obtained at 408 nm, 296 nm and
240 nm and it can be seen that these values are corresponding to
the experimental absorption ones. In addition to the results gas
phase, TD-DFT calculations of the title compound in ethanol sol-
vent were performed by using PCM model. The PCM calculations
reveal that the calculated absorption bands have slight blue-shifts
with values of 421 nm, 301 nm and 244 nm when compared with
the gas-phase calculations of TD-DFT method. Comparing these
values with the corresponding experimental values, TD-DFT meth-
Fig. 5. UV–Vis absorption spectrum of the title compound in ethanol solvent.
od for both in gas phase and solvent media is useful to predict UV–
Vis spectrum.
According to the investigation on the frontier molecular orbital
(FMO) energy levels of the title compound, we can find that the
corresponding electronic transfer happened between the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO), HOMO and LUMO + 1, HOMO ꢁ 1 and
LUMO + 1 orbitals, respectively. Fig. 4 shows the distributions
and energy levels of the FMOs computed at the B3LYP/6–
31G(d,p) level for the title compound. As seen from Fig. 6, in the
HOMO, LUMO and LUMO + 1 electrons are mainly delocalized on
the naphthalene, benzene (C12–C15) ring and the atoms of imine
group; in the HOMO ꢁ 1, electrons are delocalized on the whole
structure.
Molecular orbital coefficients analyses based on optimized
geometry indicate that, for the title compound, the frontier molec-
ular orbitals are mainly composed of p-atomic orbitals, so afore-
mentioned electronic transitions are mainly derived from the
contribution of bands n ? p⁄ and p ? p⁄.
Fig. 4. FT-IR spectrum of the title compound.

G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
75
Fig. 6. Molecular orbital surfaces and energy levels given in parentheses for the HOMO ꢁ 1, HOMO, LUMO and LUMO + 1 of the title compound computed at B3LYP/6-
31G(d,p) level.
dummy integration variable [55,56]. MEP is related to the electronic
density and is a very useful descriptor in determining sites for elec-
trophilic and nucleophilic reactions as well as hydrogen bonding
interactions [57,58]. Being a real physical property, V(r) can be
determined experimentally by diffraction or by computational
methods [59].
3.5. Energetics and stability
The NH and OH tautomerism of the title compound is given in
Scheme 1. To investigate the tautomeric stability, optimization cal-
culations at B3LYP/6-31G(d,p) level were performed for the NH
and OH forms of the title compound. Some physicochemical prop-
erties such as total, HOMO and LUMO energies, dipole moment and
The MEP at the B3LYP/6-31G(d,p) optimized geometry was cal-
culated. The negative (red)1 region of MEP was related to electro-
philic reactivity and the positive (blue) region to nucleophilic
reactivity (see Fig. 7). In the MEP, there are several possible sites
for electrophilic attack. Negative electrostatic potential regions
are mainly localized over the O1 and O2 atoms. The negative V(r)
values are ꢁ0.0544 a.u for O1 atom which is the most negative re-
gion, ꢁ0.0221 a.u for O2 atom. However, a maximum positive re-
chemical hardness (g) were also calculated with the same level of
theory and the results were given in Table 4. The chemical hard-
ness is quite useful to rationalize the relative stability and reactiv-
ity of chemical species. Hard species having large HOMO–LUMO
gap will be more stable and less reactive than soft species having
small HOMO–LUMO gap [54]. As seen from Table 4, the total en-
ergy of the OH form is lower than the NH form, while chemical
hardness of the OH form is greater than the NH one, which indi-
cates that the OH form of the title compound is more stable than
its NH form in gas phase.
In order to evaluate the solvent effect to the aforementioned
properties of the title compound, we carried out calculations in
three kinds of solvent (water, ethanol, and chloroform) with the
B3LYP/6-31G(d,p) level using the PCM model and the results are gi-
ven in Table 4. From Table 4, we can conclude that the total molec-
ular energies obtained by PCM method decrease with the
increasing polarity of the solvent, while the dipole moments and
hardness will increase with the increase of the polarity of the sol-
vent. According to these results, the stability of the title compound
increases in going from the gas phase to the solution phase.
gion is localized on
H atom bonded to C11 with a value
of +0.0322 a.u., indicating a possible site for nucleophilic attack.
According to these calculated results, the MEP map shows that
the negative potential sites are on oxygen atoms as well as the po-
sitive potential sites are around the hydrogen atoms.
3.7. Non-linear optical effects
Non-linear optical (NLO) effects arise from the interactions of
electromagnetic fields in various media to produce new fields al-
tered in phase, frequency, amplitude or other propagation charac-
teristics from the incident fields [60]. NLO is at the forefront of
current research because of its importance in providing the key
functions of frequency shifting, optical modulation, optical switch-
ing, optical logic, and optical memory for the emerging technolo-
gies in areas such as telecommunications, signal processing, and
optical interconnections [61–64]. Organic molecules that exhibit
3.6. Molecular electrostatic potential
The molecular electrostatic potential V(r) that is created in the
space around a molecule by its nuclei and electrons is well estab-
lished as a guide to molecular reactive behavior. It is defined by:
extended
p conjugation, in particular, show enhanced second order
NLO properties [65].
The total static dipole moment (l), the linear polarizability (a)
and the first hyperpolarizability (b) using the x, y, z components
Z
X
ZA
RA ꢁ r
q
ðr0Þ
VðrÞ ¼
ꢁ
dr0
ð1Þ
r0 ꢁ r
are defined as [66,67]:
A
in which ZA is the charge of nucleus A, located at RA,
q
ðr0Þ is the
1
For interpretation of color in Figs. 1–3, 6, 7 the reader is referred to the web
electronic density function of the molecule, and r0 is the
version of this article.

76
G. Alpaslan et al. / Journal of Molecular Structure 997 (2011) 70–77
Table 4
Calculated energies, dipole moments, frontier orbital energies and chemical hardness.
OH form gas phase (
e
= 1)
NH form gas phase (
e
= 1)
Chloroform (
e
= 4.9)
Ethanol (
e
= 24.55)
Water (e = 78.39)
Etotal (Hartree)
EHOMO (eV)
ELUMO (eV)
ꢁ1091.9203
ꢁ5.410
ꢁ1.830
1.790
ꢁ1091.9185
ꢁ5.280
ꢁ1.992
1.644
ꢁ1091.9323
ꢁ5.265
ꢁ1.968
1.648
ꢁ1091.9380
ꢁ5.290
ꢁ1.990
1.650
ꢁ1091.9404
ꢁ5.280
ꢁ1.977
1.651
g
(eV)
(D)
l
1.724
2.432
3.142
3.465
3.6180
Fig. 7. Molecular electrostatic potential map calculated at B3LYP/6-31G(d,p) level.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ia. Molecular orbital coefficient analyses suggest that the electronic
transitions are mainly assigned to n ? p⁄ and p ? p⁄ electronic
transitions. The total energy of the title compound decreases with
increasing polarity of the solvent. The MEP map shows that the
negative potential sites are on oxygen atoms as well as the positive
potential sites are around the hydrogen atoms. These sites may
provide information about the possible reaction regions for the ti-
tle structure. This study also demonstrates that the title compound
can be used as a good nonlinear optical material.
l
a
¼
¼
lx2
þ
ly2
þ
lz2
ð2Þ
ð3Þ
axx
þ
ayy
3
þ
azz
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2
2
b ¼ ðbxxx þ bxyy þ bxzzÞ þ ðbyyy þ bxxy þ byzzÞ þ ðbzzz þ bxxz þ byyz
Þ
ð4Þ
The dipole moment (l), linear polarizability (a) and the first
hyperpolarizability (b) were calculated at the B3LYP/6-31G(d,p) le-
vel using Gaussian 03 W program package. The calculated dipole
Supplementary data
moment (l), polarizability (a) and first hyperpolarizability (b) for
title compound are 2.432 D, 45.34 Å3 and 39.01 ꢂ 10ꢁ30 cm5/esu
respectively. The calculated values of first hyperpolarizability and
polarizability are greater than that of 4-(2,3,4-trihydroxybenzy-
lideneamino)antipyrine [60] and 2-methyl-6-[2-(trifluorormeth-
yl)phenyl-iminomethyl]phenol [67]. These results indicate that
title compound is a good candidate of nonlinear optical material.
Crystallographic data for the structure reported in this article
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication number CCDC 814002. Copies
of the data can be obtained free of charge on application to CCDC
12 Union Road, Cambridge CB21 EZ, UK (fax: +44 1223 336 033;
e-mail: data_request@ccdc.cam.ac.uk).
4. Conclusion
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