The prototropic tautomerism and substituent effect through strong electron-withdrawing group in (E)-5-(diethylamino)-2-(3-nitrophenylimino)methyl] phenol

Article abstract of DOI:10.1016/j.saa.2013.05.044

The prototropic tautomerism in o-Hydroxy Schiff bases results in two forms called phenol-imine and keto-amine. The preference of a particular form by the compound changes in the solid and solvent media. The choice can also be regulated by a substituent with a different electron-donating or withdrawing group. In the present study, the above-mentioned factors are considered in the investigation of (E)-5- (diethylamino)-2-[(3-nitrophenylimino)methyl]phenol compound (an o-Hydroxy Schiff basis) by experimental (XRD, FT-IR and UV-vis) and computational (DFT and TD-DFT) methods. The results show that the title compound adopts only phenol-imine form in the solid and solvent media. This was attributed to the substituent effect through strong electron-withdrawing nitro group.

Full text of DOI:10.1016/j.saa.2013.05.044

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 205–213
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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The prototropic tautomerism and substituent effect through strong
electron-withdrawing group in (E)-5-(diethylamino)-2-[(3-
nitrophenylimino)methyl]phenol
a
b
c
Çig˘dem Albayrak a, , Gökhan Kasßtaßs , Mustafa Odabasßog˘lu , Rene Frank
⇑
a Sinop University, Faculty of Education, 57000 Sinop, Turkey
b Pamukkale University, Chemical Technology Program, 20070 Kınıklı-Denizli, Turkey
c Leipzig University, Faculty of Chemistry and Mineralogy, D-04103 Leipzig, Germany
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
ꢀ
ꢀ
ꢀ
Prototropic tautomerism is
experimentally and theoretically
investigated.
The effect of substituent is
emphasized on proton transfer
process.
The supramolecular structure of title
compound is investigated.
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 30 May 2013
The prototropic tautomerism in o-Hydroxy Schiff bases results in two forms called phenol-imine and
keto-amine. The preference of a particular form by the compound changes in the solid and solvent media.
The choice can also be regulated by a substituent with a different electron-donating or withdrawing
group. In the present study, the above-mentioned factors are considered in the investigation of (E)-5-
(diethylamino)-2-[(3-nitrophenylimino)methyl]phenol compound (an o-Hydroxy Schiff basis) by exper-
imental (XRD, FT-IR and UV–vis) and computational (DFT and TD-DFT) methods. The results show that
the title compound adopts only phenol-imine form in the solid and solvent media. This was attributed
to the substituent effect through strong electron-withdrawing nitro group.
Keywords:
Schiff base
DFT
Computational study
Intramolecular proton transfer
FT-IR
UV–vis
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
[28–30]. Schiff bases may have thermochromic and photochromic
properties [31,32]. Their photochromic species can be used as opti-
A Schiff base consists of a functional group that contains a car-
bon–nitrogen double bond with the nitrogen atom connected to an
aryl or alkyl group [1]. Schiff bases can be formulated as
R1R2C@NR3 where R1, R2 and R3 represent aromatic or aliphatic
groups. Their preparation is through a condensation reaction of
primary amines with carbonyl compounds [1–5]. Schiff bases have
wide range of applications spanning the industrial [6–10], pharma-
ceutical [11–13], biological [14–20] and chemical fields [21–26].
For instance, they are industrially used as dyes and pigments in
textile [27] in addition to their application in pharmacology for
the synthesis of antibiotics, antiallergic and antitumor substances
cal switches and optical memories, variable electrical current, ion
transport through membranes [33]. It was reported that the
photochromism and thermochromism in Schiff bases were closely
related to the prototropic tautomerism [32,34], molecular geome-
try (being planar or non-planar) [35], the crystal packing of the
compound [35]. In addition, Schiff bases may exhibit interesting
chemical properties, depending on the substituents with different
electron-donating or electron-withdrawing groups [36]. Therefore,
the investigation of Schiff bases by considering above-mentioned
factors will contribute to general understanding of fundamental
properties in these species. (E)-5-(diethylamino)-2-[(3-nitrophe-
nylimino)methyl]phenol is a Schiff base with NO2 and diethyl-
amino groups as substituents. In the current study, the title
compound was studied with experimental (XRD, FT-IR and
⇑
Corresponding author. Tel.: +90 368 2715532; fax: +90 368 2715530.
E-mail address: calbayrak@sinop.edu.tr (Ç. Albayrak).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.05.044

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Ç. Albayrak et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 205–213
UV–vis) and computational (DFT and TD-DFT) methods by focusing
on the prototropic tautomerism, proton transfer process and sub-
stituent effect.
Computational procedure
All computations were performed by Gaussian 03W software
[41]. GaussView program was used for molecular visualization of
calculated structures [42]. The gas phase geometry optimizations
for two tautomeric structures of the title compound were carried
out at DFT level by using the hybrid functional B3LYP (Becke’s
three-parameter hybrid functional with LYP correlation functional)
[43] with 6-311G(d,p) basis set [44]. The initial structures for the
geometry optimizations were taken from X-ray measurement.
The vibrational frequencies and the non-linear optical properties
of enol form were also calculated at B3LYP level. Electronic excita-
tions of the title compound were calculated by using TD-DFT [45–
48] for gas phase. The calculation was started from optimized
geometry of the title compound in gas phase, maintaining the same
level of theory as in optimization process.
Experimental and computational methods
Synthesis
The title compound was prepared by refluxing a mixture of a
solution containing 5-(diethylamino)-2-hydroxybenzaldehyde
(0.5 g, 2.59 mmol) and
a solution containing 3-nitroaniline
(0.36 g, 2.59 mmol) in 20 mL ethanol. The reaction mixture has
been stirred for 1 h under reflux. The crystals of the title compound
suitable for X-ray analysis were obtained by slow evaporation from
acetone (yield 58%; m.p. 406–408 K).
Instrumentation
The melting point was determined by using StuartMP30 appa-
ratus. FT-IR spectrum of the title compound was recorded on a Bru-
ker Vertex 80 V spectrometer using KBr pellet. UV–vis absorption
spectra were recorded on a Thermo scientific BioGenesis UV–vis
spectrometer using a 1 cm path length of the cell. NMR spectra
were recorded on 300 MHz Bruker spectrometer.
Results and discussion
Molecular structure from experimental and computational
standpoints
The title compound contains NO2 and diethylamino groups as
substituents. It adopts eclipsed conformation referring to its ethyl
groups. The related torsion angles [C4AN2AC14AC15 = ꢁ74.7(2)°
and C4AN2AC16AC17 = 84.0(2)°] have comparable values with
those observed in the compounds with methyl [49], iodine [50]
and bromine [51] substituents. o-Hydroxy Schiff bases show proto-
tropic tautomerism via intramolecular proton transfer between the
phenolic oxygen and imino nitrogen atoms. The process of proton
transfer ends up with two tautomeric forms known as enol and
keto structures. These are illustrated for the title compound in
Fig. 1. Previous studies showed that o-Hydroxy Schiff bases can ex-
ist in one or both of these forms in the solid state [52–54]. XRD
study reveals the preference of enol structure by the title com-
pound in the solid state (Fig. 2). The enol form of the title com-
pound can also be inferred from the harmonic oscillator model of
X-ray crystallography
XRD data were collected at 130 K with an Xcalibur diffractom-
eter using Mo K radiation. The crystal structure was solved by di-
a
rect methods using SHELXS-97 [37]. All non-hydrogen atoms were
refined anisotropically by full matrix least-squares methods [37].
The H atoms were located in a difference Fourier map. Their coor-
dinates and Uiso(H) values were refined freely [OAH = 0.92(2) Å
and CAH = 0.96(2)–1.01(2) Å]. WinGX [38], ORTEP-3 for Windows
[39] and MERCURY [40] softwares were used for molecular draw-
ings and other materials. Relevant crystal data, experimental con-
ditions and final refinement parameters can be obtained from
Cambridge Structural Database (CCDC: 809224).
Fig. 1. The enol and keto forms of the title compound.
Fig. 2. Crystallographically obtained molecular structure of the title compound.

Ç. Albayrak et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 205–213
207
Table 1
(1.298(2) Å) distances indicate the single and double bond character
of these bonds, respectively. Their counterparts in the optimized
structure are 1.339 Å and 1.296 Å.
Hydrogen bond interactions (Å, °) in the title compound.
DAHꢂꢂꢂA
d(DAH)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
<DAHꢂ ꢂ ꢂA
The compound adopts E configuration with respect to the C@N
double bond. The strong intramolecular interaction involving phe-
nolic atom (O1) and nitrogen atom (N1) constitutes an S(6) ring
[59,60]. This H-bond is characterized by O1ꢂ ꢂ ꢂN1 distance of
2.594 Å (Table 2), being shorter than the sum of the van der Waals’
radii for N and O [61]. It is known that there is a strong correlation
between the strength of the H-bond and the delocalization of the
system of conjugated double bonds, and the effect is qualitatively
interpreted by resonance-assisted hydrogen bond (RAHB) model
[62]. The observed Oꢂ ꢂ ꢂN distance (2.594 Å) for the title compound
are significantly shorter than 2.656 Å which was reported for
OAHꢂ ꢂ ꢂN in the class of RAHB [63]. The possibility for the title com-
pound to exhibit thermochromic or photochromic properties is re-
lated respectively to its planar or non-planar geometry which can
be determined by the dihedral angle between C1/C6 and C9/C14
rings [32]. The experimental value for the dihedral angle is 28.1°
while the computed one is 38.5°. Both results indicate possible
appearance of photochromic properties.
C15AH15Bꢂ ꢂ ꢂO3i
C17AH17Bꢂ ꢂ ꢂO2ii
C5AH5ꢂ ꢂ ꢂO2iii
1.02(2)
1.02(2)
1.00(2)
0.97(2)
0.92(2)
2.67(2)
2.55(2)
2.69(2)
2.59(2)
1.74(2)
3.533(2)
3.560(2)
3.547(2)
3.263(2)
2.594(2)
142.3(14)
169.2(13)
143.3(14)
126.5(12)
152.0(18)
C10AH10ꢂ ꢂ ꢂO1iv
O1AH1ꢂ ꢂ ꢂN1
Symmetry codes: (i) ꢁ1/2 + x, 1/2 ꢁ y, ꢁ1/2 + z, (ii) 2 ꢁ x, y, 3/2 ꢁ z, (iii) 3/2 ꢁ x, ꢁ1/
2 + y, 3/2 ꢁ z, (iv) 2 ꢁ x, ꢁ1 + y, 3/2 ꢁ z.
aromaticity (HOMA) index by using the following equation for the
rings [55,56]:
"
#
n
X
a
n
2
HOMA ¼ 1 ꢁ
ðRi ꢁ Ropt
Þ
ð1Þ
i¼1
where n is the number of bonds in the ring,
a
is a constant equal to
257.7 and Ropt is equal to 1.388 Å for CC bonds. For purely aromatic
compounds, HOMA index is equal to 1 while it is equal to 0 for non-
aromatic compounds. The HOMA indices in the range of 0.900–
0.990 and 0.500–0.800 correspond to aromatic and the non-aro-
matic rings, respectively [57,58]. In the current study, the calculated
HOMA indices for C1/C6 and C8/C13 rings are 0.898 and 0.990,
respectively. These results show that C8/C13 and C1/C6 rings in
the title compound have purely aromatic character. The computa-
tional study was performed at DFT/B3LYP level for further analysis
on the molecular structure of title compound. The discrepancies be-
tween XRD and DFT structures were analyzed quantitatively by
R.M.S. overlay. The R.M.S. fit based on atomic positions is 0.203 Å,
indicating the agreement between the two structures (Table S1).
The experimental values for C2AO1 (1.360(2) Å) and C7AN1
Table 2
The energies and dipole moments of enol and keto forms.
Enol form
Keto form
Etot (a.u.)
(D)
ꢁ1049.35887155
9.1473
ꢁ1049.35078159
8.6188
l
ELUMO (eV)
EHOMO (eV)
ꢁ2.435
ꢁ2.731
ꢁ5.628
ꢁ5.583
D
E (eV)
3.193
2.852
Fig. 3. The gradual demonstration of the formation of 2D sheet structures in (010) and parallel planes.

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Fig. 4. Relative energy profile during the proton transfer process.
2D sheet structures in (010) and parallel planes (Fig. 3c). From
topologic point of view, each discrete molecule in the 2D sheet
can be considered as a node. In this sense, each node is connected
to four nodes. As a result, a 2D topologic structure (a square grid) is
formed, which is defined as (4,4)-net in Wells nomenclature or
(4462) in Schläfli notation [64]. (iv) The increase in the dimension-
ality of the network is provided by another interaction of CAHꢂ ꢂ ꢂO
type. More specifically, the 2D sheets in Fig. 3c are inter-connected
by C10AH10ꢂ ꢂ ꢂO1iv (iv: 2 ꢁ x, ꢁ1 + y, 3/2 ꢁ z) interactions to con-
struct 3D structure of the network.
The intramolecular proton transfer process in gas phase
The total energies, dipole moments and the highest occupied
molecular orbital (HOMO) and the lowest-lying unoccupied molec-
ular orbital (LUMO) energies of enol and keto structures are given
in Table 2. Comparing the total energies of the two tautomers, the
enol form is more stable than the keto form by 5.08 kcal/mol. This
is an expected result since the enol form has two aromatic rings
and o-Hydroxy Schiff bases generally prefer the enol structure.
The intramolecular proton transfer was investigated in the gas
phase for the title compound by performing a PES scan process
at the B3LYP/6-311G(d,p) level in order to determine its effects
on the molecular geometry. The process was started from opti-
mized enol geometry by selecting O1AH1 bond as redundant inter-
nal coordinate. The graph of the relative energy versus the O1AH1
bond distances is given in Fig. 4. The energy values were calculated
relative to the energy of stable enol form. Fig. 4 shows two minima
representing the stable forms. In the figure, the keto form corre-
sponds to a local minimum while the global minimum represents
the stable enol form. The potential energy needed for the transition
from enol form to keto form was calculated as 6.53 kcal/mol.
The molecular geometry and its relevance to the intramolecular
proton transfer can also be examined by considering the changes in
HOMA index of C1/C6 ring and indicative bond lengths for each
step in the scan process. The changes in C2AO1, C1AC7 and
C7AN1 bond lengths during the transfer process are shown in
Fig. 5. The bond lengths of stable enol form, C2AO1 (1.339),
C1AC7 (1.432) and N1AC7 (1.296) were found as 1.264, 1.384
Fig. 5. The changes in C2AO1, C1AC7 and C7AN1 bond lengths during the proton
transfer process.
The 3D supramolecular structure of the title compound is self-
assembled through CAHꢂ ꢂ ꢂO interactions (Table 1) between CAH
(aliphatic and aromatic), phenol and NO2 groups with the follow-
ing
molecular
arrangement:
(i)
The
intermolecular
C15AH15Bꢂ ꢂ ꢂO3i (i: ꢁ1/2 + x, 1/2ꢁy, ꢁ1/2 + z) H-bonds connect
adjacent molecules to form an undulating C(15) chain along
[101] (Fig. 3a). (ii) The chains formed in this way are further con-
nected by C17AH17Bꢂ ꢂ ꢂO2ii (ii: 2 ꢁ x, y, 3/2 ꢁ z) interactions
(Fig. 3b), resulting in a tape structure with R44ð20Þ [59,60] synthons
located at (1/4 + n, 1/4, n; n = 0 or half-integer) positions. (iii) Fur-
ther analysis shows that the tape structures are mutually linked by
C5AH5ꢂ ꢂ ꢂO2iii (iii: 3/2 ꢁ x, ꢁ1/2 + y, 3/2 ꢁ z) interactions to form

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209
and 1.340 Å at the fifteenth step of scan where the stable keto tau-
tomer was observed. It is seen that the intramolecular proton
transfer affects the double and single characters of these indicative
bonds. The HOMA index of C1/C6 ring was calculated at each step
of the scan process. The change of HOMA index in terms of scan
coordinate is shown in Fig. 6. As expected, the aromaticity level
of C1/C6 ring decreases with the scan coordinate from 0.9 to 1.6 Å.
UV–vis absorption spectra
Experimental UV–vis spectra of the title compound in three
organic solvents of different polarities (Benzene, DMSO and
EtOH) are shown in Fig. 7. An absorption band near 360 nm in
three solvents is observed. The absorption band for the keto-
amine form occurs above 400 nm with respect to previous
experimental and computational results [65,66]. The experimen-
tal spectra of the title compound show no absorption peak in
this region. Considering the absence of a peak above 400 nm, it
can be said that the title compound adopts only phenol-imine
form in solution. Previous experimental studies indicate that
some compounds including N,N-diethyl amino group exist in
both phenol-imine and keto-amine forms in EtOH [49–51]. How-
ever, the title compound exists in only phenol-imine form in
EtOH. This result can be attributed to the powerful electron-
withdrawing nature of the nitro group (ANO2). The strong elec-
tron-withdrawing nitro group with inductive effect withdraws
Fig. 7. UV–vis spectra of the title compound in DMSO, EtOH and benzene.
tained by using SWizard Program [68]. The results show that the
two important excitation energy values with oscillator strength
(f) larger than 0.16 are located at 349.2 nm [HOMO ? LUMO+1
(48%), HOMOꢁ1 ? LUMO (16%)] and 350.7 nm [HOMOꢁ1 ? LU-
MO (82%), HOMO ? LUMO+1 (13%)]. Considering TD-DFT calcula-
tions, it can be said that the excitation energy value near 360 nm
arises from HOMO ? LUMO+1 and HOMOꢁ1 ? LUMO transitions
of the title compound.
electron density from
p system of ring it is bonded to and de-
creases the electron density on nitrogen atom of imino group.
Therefore, such an effect makes the formation of keto-amine
form difficult even in solution.
HOMO and LUMO orbitals play an important role in reaction be-
tween molecules and in electronic spectrum of a molecule [67].
The frontier molecular orbitals of title compound were given in
Fig. 8. The first 10 spin-allowed singlet–singlet excitations for the
title compound were calculated by TD-DFT approach. TD-DFT cal-
culations started from optimized geometry were performed for
gas phase to calculate excitation energies. The percentage contri-
butions of molecular orbitals to the formation of bands were ob-
FT-IR spectroscopy
The experimental and calculated FT-IR spectra of the title com-
pound are given in Fig. 9. The calculations were performed at
Fig. 6. The changes in HOMA index of C1/C6 ring during the proton transfer process.

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The OAH stretching vibration was calculated to be at
3133 cmꢁ1
However, this mode was observed at 3000–
.
1700 cmꢁ1 in the experimental spectrum since it is broadened by
the strong intramolecular hydrogen bond between C@N and OAH
groups. It was reported that the two bands around 1550–1500
and 1360–1290 cmꢁ1 correspond to asymmetrical and symmetri-
cal stretching vibrations of aromatic nitro group, respectively
[71]. These modes are observed at 1520 and 1353 cmꢁ1 experi-
mentally and at 1548 and 1337 cmꢁ1 computationally. The asym-
metrical and symmetrical stretching vibrations of methylene
groups occur near 2926 and 2853 cmꢁ1 while those of methyl
groups are near 2962 and 2872 cmꢁ1, respectively [71]. Corre-
sponding vibrations of methylene and methyl groups in the title
compound are observed at 2977, 2936 and 2890 cmꢁ1. B3LYP re-
sults for these vibrations are 2973, 2948, 2943, 2938, 2936 cmꢁ1
.
The bending vibrations of methyl and methylene groups in the title
compound are at 1450, 1424 and 1382, 1301 cmꢁ1, respectively.
The calculated values are 1458, 1453, 1449, 1444, 1440, 1369,
1364, 1302 cmꢁ1. The typical aromatic C-H bands of the title com-
pound are at 3084 cmꢁ1, and calculated results span the range
3057–3129 cmꢁ1. The strong peak at 1629 cmꢁ1 in experimental
spectrum has been attributed to C@N stretching vibration. This
mode was calculated to be 1611 cmꢁ1. The absorption bands at
1600–1585 cmꢁ1 and 1500–1400 cmꢁ1 arise from skeletal vibra-
tions, involving CAC stretching within the aromatic ring [71].
The CAC stretching modes of aromatic rings of the title compound
were observed at 1594, 1575 cmꢁ1. Skeletal vibrations at 1500–
1400 cmꢁ1 overlap stretching vibration of the nitro group.
Fig. 8. The frontier molecular orbitals of title compound in gas phase.
B3LYP/6-311G(d,p) theory level and resulting frequencies were
scaled by 0.9682 [69] in order to correlate experimental and com-
putational results. In addition, the calculated frequencies were
investigated with VEDA 4 program by considering PEDs [70]. The
experimental and the calculated frequencies were given in
Table S2 comparatively.
NMR spectra
The 1H NMR spectrum of the title compound was recorded in
CDCl3 (Fig. 10). The resonance of hydroxyl proton is at 13.19 ppm
which is typical for intramolecular hydrogen bonding (OAHꢂ ꢂ ꢂN)
proton. The resonance of imino proton is at 8.48 ppm.
Fig. 9. The comparison of experimental (a) and calculated (b) FT-IR spectra of the title compound.

Ç. Albayrak et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 205–213
211
Fig. 10. 1H NMR spectrum of the title compound in CDCl3.
In 1H NMR spectrum of the title compound, the absorption
peaks of aromatic ring protons are between and 8 ppm
Non-linear optical (NLO) properties
6
(Fig. 10). The H3 proton is coupled to the H5 proton and shows
doublet peaks at 6.20 ppm (J3,5 = 2.4 Hz). The H5 proton coupled
to H6 shows doublet and gives another doublet by coupling H3
as being 6.29 ppm (J5,6 = 9 Hz, J5,3 = 2.4 Hz).The H6 proton is cou-
pled to the H5 proton and shows doublet at 7.20 ppm
(J6,5 = 9 Hz). The H10 proton is coupled to the H11 and H9 protons
and give the triplet at 7.28 ppm (J10,11 = J10,9 = 8.1). The H11 proton
coupled to H10 shows doublet and gives triplet by coupling H13
and H9 as being 8.03 (J11,10 = 8.1 Hz, J11,13 = J11,9 = 2.4 Hz). The H9
proton coupled to H10 shows doublet and gives triplet by coupling
H11 and H13 as being 7.51 ppm (J9,10 = 8.1 Hz; J9,11 = J9,13 = 2.4 Hz).
The H13 proton is coupled to the H11 and H9 protons and shows
triplet at 8.07 ppm (J13,11 = J13,9 = 2.4 Hz). H14 protons couple to
H15 protons, they give a quartet (3.42 ppm, J14,15 = 7.2 Hz) and a
triplet (1.22 ppm, J15,14 = 7.2 Hz) (Fig. 10), respectively. These re-
sults are in accordance with the literature values [71]. The absorp-
tion of ring protons is in the range of 6–8 ppm which corresponds
to aromatic character. This result reveals that the title compound
adopts enol form in solution.
The non-linear optical properties have an important role for the
design of materials, in modern communication technology, signal
processing, optical switches and optical memory devices [72].
The non-linear optical properties of the organic molecules ensue
from delocalized
p electrons that move along molecule. The in-
crease of the conjugation on molecule results in an increase in its
non-linear optical properties. Addition of donor and acceptor
groups also increases non-linear optical properties of a molecule.
If the donor and acceptor groups are powerful, delocalization of
p
electron cloud on organic molecules increases and as a result
of this the polarizability and first hyperpolarizability of organic
molecules increase [73]. The title compound, a Schiff Base has
the delocalized
p electron system. In order to investigate the effect
of electron system and donor–acceptor group on its non-linear
p
optical property was computationally studied by DFT (B3LYP) the-
ory level.
The average linear polarizability
a, and the first hyperpolariz-
ability b can be calculated by using the Eqs. (2), (3), respectively
[72].
In the 13C NMR spectrum of the title compound recorded in
CDCl3 (Fig. 11), the imino carbon (C7) peak was observed at
162.401 ppm, and the phenolic carbon (C2) peak appeared at
163.744 ppm. The 13C NMR spectrum of the title compound shows
peaks at 152.427 ppm (C8), 150.551 ppm (C4) and 149.071 ppm
(C12). The C1, C3, C5 and C6 carbons of aromatic ring are at
108.730 ppm, 97.504 ppm, 104.245 ppm and 134.439 ppm, respec-
tively. The C13, C11, C10 and C9 carbons are at 115.074 ppm,
119.803 ppm, 129.945 ppm and 127.871 ppm, respectively. The
CH2 (C14) and CH3 (C15) peaks of ethyl group are seen at
44.702 ppm and 12.688 ppm, respectively (Fig. 11). The results
agree well with the reported values [71].
a
¼ 1=3ðaxx
þ
ayy
þ
azz
Þ
ð2Þ
2
2
b ¼ ½ðbxxx þ bxyy þ bxzzÞ þ ðbyyy þ bxxy þ byzzÞ þ ðbzzz þ bxxz
2
1=2
þ byyzÞ ꢃ
ð3Þ
The polarizability and the first hyperpolarizability were calculated
at the level of B3LYP/6-311G(d,p) and the calculated results are gi-
ven in Table 3.
The calculated polarizability (a) and first hyperpolarizability (b)
of title compound are 40.73 Å3 and 57.15 ꢄ 10ꢁ30 cm5/esu that are
greater than those of urea (
a
and b of urea of 3.8312 Å3 and

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Fig. 11. 13C NMR spectrum of the title compound in CDCl3.
Table 3
form. It is concluded on the basis of UV–vis studies that the title
compound adopts only phenol-imine form in three organic sol-
vents of different polarities (Benzene, DMSO and EtOH). The result
was attributed to the substituent effect through strong electron-
withdrawing nitro group. The UV–vis results are also correlated
with those of time-dependent density functional theory (TD-
DFT). The investigation of non-linear optical properties suggests
that the title compound can be used as a non-linear material.
Calculated polarizability and first hyperpolarizability components (a.u.) for the title
compound.
axx
axy
ayy
axz
ayz
azz
484.2728381
12.7349048
215.4352025
13.5826842
4.7702881
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
6732.3617728
954.6803769
ꢁ73.9420964
ꢁ70.4908562
119.0814365
236.0247558
ꢁ23.5312242
ꢁ107.8030919
25.8574634
125.6323023
Appendix A. Supplementary material
ꢁ10.1765636
Crystallographic data for the structure in this paper have been
deposited with the Cambridge Crystallographic Data Centre as
the supplementary publication no. CCDC 809224. Copies of the
data can be obtained, free of charge, on application to CCDC, 12 Un-
ion Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk). Tables S1 and S2 are also provided. Sup-
plementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.saa.2013.05.044.
0.37289 ꢄ 10ꢁ30 cm5/esu), respectively [74]. In addition, it is found
that the first hyperpolarizability of title compound is greater than
those of related Schiff bases [75,76]. The strong electron withdraw-
ing ANO2 group and electron-donating N,N-diethylamino group
increase the movement of
p electron cloud. This leads to an in-
crease in conjugation and consequently an increase in non-linear
optical properties. The results show that the title compound can
be used as a good non-linear optical material.
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