Experimental and theoretical DFT studies of structure, spectroscopic and fluorescence properties of a new imine oxime derivative

Article abstract of DOI:10.1016/j.molstruc.2012.05.032

A new imine oxime, (1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime (I), is synthesized and characterized. The title compound crystallizes in the monoclinic space group P2₁/c with a = 12.3416(7), b = 9.5990(6), c = 11.9750(7), β = 92.417(4) and Z = 4. Crystallographic, vibrational (IR), and NMR (¹H and ¹³C chemical shifts) data are compared with the results of density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. The structure of I is stabilized by intermolecular OH...N hydrogen bonds. The theoretical calculations show that the compound exhibits a number of isomers, and the molecular geometry of the most stable optimized isomer (s-trans-E,E) can well reproduce the X-ray structure. The calculated vibrational bands and NMR chemical shifts are consistent with the experimental results. The NBO/NPA atomic charges are performed to explore the possible coordination modes of the compound. The electronic (UV-vis) and photoluminescence spectra calculated using the TD-DFT method are correlated to the experimental spectra. The DMSO solutions of I are fluorescent at room temperature. The assignment and analysis of the frontier HOMO and LUMO orbitals indicates that both absorption and emission bands are originated mainly from the π-π transitions.

Full text of DOI:10.1016/j.molstruc.2012.05.032

Journal of Molecular Structure 1024 (2012) 65–72
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Experimental and theoretical DFT studies of structure, spectroscopic
and fluorescence properties of a new imine oxime derivative
b
c
Yunus Kaya a, Veysel T. Yilmaz a, , Taner Arslan , Orhan Buyukgungor
⇑
a Department of Chemistry, Faculty of Arts and Sciences, Uludag University, 16059 Bursa, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey
c Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, 55139 Samsun, Turkey
h i g h l i g h t s
"
"
"
"
(1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime was synthesized and characterized by IR, UV–vis, NMR and X-ray crystallography.
The structure of the title compound is stabilized by intermolecular OAHÁ Á ÁN hydrogen bonds.
Molecular geometry and conformations were determined by DFT method.
The compound in DMSO is fluorescent at room temperature.
a r t i c l e i n f o
a b s t r a c t
Article history:
A new imine oxime, (1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime (I), is synthesized and charac-
terized. The title compound crystallizes in the monoclinic space group P21/c with a = 12.3416(7),
b = 9.5990(6), c = 11.9750(7), b = 92.417(4) and Z = 4. Crystallographic, vibrational (IR), and NMR (1H
and 13C chemical shifts) data are compared with the results of density functional theory (DFT) method
at the B3LYP/6-311++G(d,p) level. The structure of I is stabilized by intermolecular OAHÁ Á ÁN hydrogen
bonds. The theoretical calculations show that the compound exhibits a number of isomers, and the
molecular geometry of the most stable optimized isomer (s-trans-E,E) can well reproduce the X-ray struc-
ture. The calculated vibrational bands and NMR chemical shifts are consistent with the experimental
results. The NBO/NPA atomic charges are performed to explore the possible coordination modes of the
compound. The electronic (UV–vis) and photoluminescence spectra calculated using the TD-DFT method
are correlated to the experimental spectra. The DMSO solutions of I are fluorescent at room temperature.
The assignment and analysis of the frontier HOMO and LUMO orbitals indicates that both absorption and
Received 28 March 2012
Received in revised form 8 May 2012
Accepted 9 May 2012
Available online 17 May 2012
Keywords:
Oxime
X-ray structure
DFT calculations
Isomerization
Spectroscopy
Photoluminescence
emission bands are originated mainly from the
p–
pà transitions.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
The imine–oximes are Schiff bases of carbonyl–oximes, usually
acting as bidentate ligands through the oxime and imine nitrogen
atoms. Upon complexation, the oxime hydrogen may or may not
dissociate. It was suggested that the coordination geometry of
the simple imine–oximes in metal complexes of the type [M(L)2]
(M = CoII, NiII and CuII) is trans-square-planar, but the octahedral
geometry occurs in the case of additional ligands such as Cl, I
and SCN at axial positions [1].
Due to broad interest in oximes, their structure, reactivity and
metal complexing capability have been investigated and well
documented in the literature [1–7]. Furthermore, the theoretical
studies on isomerizations [15–28], reaction mechanisms [29–32]
and spectroscopic characteristics (UV–vis, IR, Raman and NMR)
[33–41] of some oximes were also performed. However, to the best
of our knowledge, no theoretical study was present on the imine–
oximes. The aim of this work is to study the molecular structure,
possible isomers and spectroscopic characterization of a new
The syntheses, structural properties, analytical applications,
solution and coordination chemistry of oximes and their metal com-
plexes have been extensively studied and described in great detail
[1–7]. Oximes as ligands played a significant role in the develop-
ment of transition metal chemistry. Since the oxime group pos-
sesses two potential coordinating donor sites such as the nitrogen
and oxygen atoms, these compounds usually exhibit an ambiden-
tate coordination behavior. However, in most cases, the coordina-
tion occurs via the nitrogen atom. Some oximes showed versatile
antimicrobial activity [8–10], while some platinum(II) complexes
of oximes exhibited high DNA binding affinity as well as significant
cytotoxic activity [11–14].
⇑
Corresponding author.
E-mail address: vtyilmaz@uludag.edu.tr (V.T. Yilmaz).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.032

66
Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
Table 1
imine–oxime, namely (1E,2E)-phenyl-[(1-phenylethyl)imino]-eth-
anal oxime (I). For this purpose, density functional theory (DFT)
calculations were performed to explain the structural and spectral
characteristics of the compound. Molecular structure parameters,
vibrational frequencies and NMR chemical shifts of the title
compound have been calculated by B3LYP/6-311++G(d,p) level of
theory and compared with the experimental data. HOMO, LUMO
and UV spectral analysis have been used to elucidate the electronic
transitions within the molecule. In addition, the photolumines-
cence properties of the compound were investigated.
Crystallographic data and structure refinement for compound I.
I
Formula
C16H16N2O
252.31
298(2)
0.71073 Å
Monoclinic
P21/c
Molecular weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
a (Å)
12.3416(7)
9.5990(6)
b (Å)
c (Å)
11.9750(7)
92.417(4)
1417.38(15)
4
1.182
0.075
b (°)
2. Experimental
Volume (Å3)
Z
2.1. Materials and measurements
Calculated density (g/cm3)
l
(mmÀ1
)
F(000)
h Range (°)
Index ranges
536
All reagents used for the synthesis of the compound are commer-
cially available and were used without further purification. Elemen-
tal analyses for C, H, and N were performed using a EuroEA 3000
CHNS elemental analyser. UV–vis spectra were measured on a Per-
1.65–28.03
À15 6 h 6 15, À12 6 k 6 12,
À14 6 l 6 14
12,659
2932 [Rint = 0.0281]
2124
Integration
0.9891 and 0.9513
2932/177
Reflections collected
kin-Elmer Lambda 35 UV/vis spectrophotometer using 1 Â 10À5
M
Independent reflections
Reflections observed (>2
Absorption correction
r
)
EtOH solutions in the 200–800 nm range. IR spectra were recorded
on a Thermo Nicolet 6700 FT-IR spectrophotometer as KBr pellets in
the frequency range 4000–400 cmÀ1. 1H NMR and 13C NMR spectra
were recorded on a Varian Mercuryplus spectrometer. Excitation
and emission spectra of 1 Â 10À3 M DMSO solutions were recorded
at room temperature with a Varian Cary Eclipse spectrophotometer
equipped with a Xe pulse lamp of 75 kW.
Max. and min. transmissions
Data/parameters
Goodness-of-fit on F2
1.0659
Final R indices [I > 2
r
(I)]
R1 = 0.0395
wR1 = 0.1054
0.106 and À0.108
Largest diff. peak and hole (e ÅÀ3
)
The absorption spectra of the complexes in EtOH were calcu-
lated based on the optimized singlet-states using restricted time-
dependent DFT (TD-DFT) with the Polarizable Continuum Model
(PCM) using the integral equation formalism variant (IEFPCM) at
the B3LYP/LanL2DZ level, while the optimized triplet excited-
states were used for the emission spectral analysis, using unre-
stricted time-dependent DFT (TD-DFT). GaussSum was used to cal-
culate group contributions to the molecular orbitals and to
simulate the UV–vis absorption and fluorescence emission spectra
[49].
2.2. Synthesis
1-Phenylethylamine (0.61 g, 5 mmol) dissolved in 5 mL EtOH
was added dropwise in a 10 mL EtOH solution of isonitrosoace-
tophenone (0.75 g, 5 mmol) and the resulting solution was stirred
at room temperature for 3 h. Well-shaped prisms of I were ob-
tained by slow evaporation at room temperature within 3 days.
Yield 61%. Mp. 136 °C. Anal. Calcd. C16H16N2O: C, 76.16; H, 6.34;
N, 11.10. Found: C, 76.36; H, 6.29; N, 10.98.
2.3. X-ray crystallography
3. Results and discussion
The intensity data of I were collected using a STOE IPDS 2 dif-
3.1. Description of the crystal structure
fractometer with graphite-monochromated Mo
Ka radiation
(k = 0.71073 Å). The structures were solved by direct methods
and refined on F2 with the SHELX-97 program [42]. All non-hydro-
gen atoms were found from the difference Fourier map and refined
anisotropically. Hydrogen atoms bonded to C atoms were refined
using a riding model, while the hydroxyl hydrogen atom is refined
freely. The details of data collection, refinement and crystallo-
graphic data are summarized in Table 1.
The molecular structure of I is shown in Fig. 1, and the bond
lengths and angles are given in Table 2. The compound crystallizes
in the monoclinic space group P21/c with four molecules in the unit
cell. The title compound is chiral and the crystal structure contains
both enantiomers. Compound I not planar and the overall molecu-
lar conformation can readily be defined in terms of the torsion an-
gles. As expected, the phenyl moieties are planar and almost
perpendicular to each other with a dihedral angle of 89.44(3)°.
The C9AN1AC7 unit combining both phenyl groups has a angle
of 121.05(10)°. The bond distances in Table 2 show that the double
bonds in the molecule are localized between the C9 and N1, and
C10 and N2 atoms, resulting in bond lengths of 1.2797(15) and
1.2747 Å, respectively, which are significantly shorter than the
C7AN1 single bond with a length of 1.4695(16) Å. The C@N bond
distances in the title compound are comparable to the correspond-
ing bonds found in the similar oxime derivatives [50,51]. The mol-
ecules of I are linked by OAHÁÁÁN (symmetry code: Àx + 1, y + 1/
2, Àz + 1/2) intermolecular hydrogen bonds involving the hydroxyl
hydrogen atom and the imine N atom. The hydrogen bonds result
in a one-dimensional chain running along the b axis and these
chains are held together by van der Waals interactions forming a
three-dimensional network.
2.4. Theoretical methods
All the calculations are performed by using GAUSSVIEW molec-
ular visualization program [43] and GAUSSSIAN 03 program
package [44]. The calculations have been carried out at DFT using
the hybrid B3LYP approach [45] and the 6-311++G(d,p) basis set.
The vibrational frequencies of the molecule were carried out for
the complete equilibrium geometry obtained by the same quantum
chemical model in the gas phase. The frequency values computed at
these levels contain known systematic errors and therefore, scaling
factors 0.958 [46] and 0.978 [47] were used for 4000–1700 cmÀ1
and 1700–400 cmÀ1 ranges, respectively. 1H and 13C NMR chemical
shifts of the compound were calculated using the GIAO method [48]
in DMSO-d6 and TMS as a reference.

Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
67
Fig. 1. Molecular view of compound I. (a) X-ray structure and (b) optimized structure of the trans-E,E isomer.
3.2. Isomerization and optimized geometry
discrepancy mainly arises from a rotation around the C1AC7 bond.
The calculated dipole moments of the isomers of title compound are
also presented in Table 3. It should be noted that the dipole mo-
ments are very much sensitive to the conformation of the isomers.
The oximes show geometrical isomerism due to rotation of the
C@N bond. The structure of I is very flexible and represents several
conformations as illustrated in Fig. 2. To establish the most stable
conformation, the molecule was subjected to a rigorous conforma-
tion analysis around the free rotation bonds. Since the calculated
dihedral angles between the planes of the double bonds in Table 3
clearly indicate that they are not coplanar in the calculated
structures, the cis and trans conformations of E- and Z-isomers can
more appropriately be called as s-cis (cisoid) and s-trans (transoid)
[52,53]. The energies of the studied isomers are listed in Table 3.
In the gas phase, the s-trans-E,E isomer is the most stable one, while
the s-trans-Z,Z isomer is the less stable. The other isomers (s-cis-E,E,
s-cis-Z,Z and s-E,Z) lie between the s-trans-E,E and s-trans-Z,Z
isomers. These findings agree well with the reported results on
the isomerization of oximes [15,20,54,55]. The molecular geome-
tries of the most stable isomer (s-trans-E,E) and the title compound
shows conformational discrepancies. The most notable mismatch is
observed in the orientation of the phenyl rings. The experimental
dihedral angle between these rings is 89.44(3)°, whereas it was
calculated as 28.58(2)° for the s-trans-E,E isomer. The present
3.3. Atomic charges
The NBO/NPA atomic charges [56,57] were calculated using the
B3LYP/6-311G++(d,p) base set. The results are listed in Table 4.
Most of the carbon atoms, except the C9 and C10 atoms, contain
negative charges and the NBO charges on the carbon atoms range
from À0.029 to À0.556 atomic charge unit (a.ch.u.). However, the
methyl carbon atom (C8) is the most negative carbon atom. The
C9 and C10 atoms to the N atoms have positive charges of 0.231
and 0.033, respectively. Both N atoms have negative charges, but
the N1 atom is much more negative the imine N atom (N2),
suggesting it as a possible donor to metal ions. On the other hand,
the O atom of the hydroxyl group have a significant negative
charge (À0.548 a.ch.u.) and the O atom also serves as another coor-
dinating site to metal ions. The NBO charges clearly indicate that
the title compound can act as a bidentate ligand through the N1
and hydroxyl O atoms.

68
Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
Table 2
the experimental values. The experimental C@N bands were
observed at 1612 and 1597 cmÀ1 as sharp bands and the calculated
values of this mode were somewhat shifted to the higher frequency
appearing at 1646 and 1629 cmÀ1. The calculated C@C stretching
band of the phenyl rings at 1606 cmÀ1 was practically not observed
experimentally. However, their d(C@C) and d(C@C) modes occurred
at 1022 and 704 cmÀ1 as coupled with other vibrational modes of I.
In addition, the CAC stretching vibrations were observed at 1069
and 1022 cmÀ1, and calculated at 1092 and 998 cmÀ1. Although
the calculated vibrational frequencies in some cases significantly
deviate from the experiment, the correlation is very linear
(r2 = 0.9954).
Geometric parameters of compound I.
Parameter
X-ray
B3LYP/6-311++G(d,p)
Bond length (Å)
C1AC2
C2AC3
C3AC4
C4AC5
C5AC6
C1AC6
C1AC7
C7AC8
C9AC10
C9AC11
C11AC12
C12AC13
C13AC14
C14AC15
C15AC16
C11AC16
C7AN1
1.385(19)
1.379(3)
1.356(3)
1.384(4)
1.388(3)
1.378(2)
1.512(2)
1.521(2)
1.461(17)
1.494(16)
1.367(2)
1.382(2)
1.351(3)
1.363(3)
1.388(2)
1.371(2)
1.470(16)
1.280(15)
1.275(15)
1.382(13)
0.890(2)
1.397
1.395
1.393
1.395
1.394
1.399
1.525
1.541
1.476
1.502
1.398
1.393
1.394
1.394
1.394
1.399
1.461
1.280
1.276
1.396
0.964
3.5. NMR spectra
Experimental and calculated 1H and 13C NMR spectra in DMSO-
d6 with TMS as a reference are illustrated in Fig. 3 and the chemical
shifts are given in Table 6. The numbering of the atoms is the same
as in Fig. 1. As can be seen from Table 6, the NMR shifts obtained by
the DFT method at the B3LYP/6-311++G (d,p) level are in reason-
able agreement with the experimental values of the 13C NMR spec-
trum. The 1H NMR spectrum is not well correlated with the
calculated spectrum, since calculations are referred to the static
molecule [59,60]. The deuterium exchangeable proton of the
hydroxyimino group (AC@NAOH) shows a characteristic chemical
shift at 11.79 ppm as singlet. The protons of the methyl group give
a doublet at 1.32 ppm. The multiple peaks between 7.10 and
7.22 ppm represent the aromatic protons of the phenyl group
(C2AC6), while the other phenyl group (C12AC16) is less shielded,
giving chemical shifts in the range of 7.26–7.44 ppm. On the other
hand, the C10AH proton is observed as a singlet at 7.88 ppm and
the C7AH signal appears at 4.43–4.48 ppm as a quartet.
C9AN1
C10AN2
N2AO1
O1AH
Bond angle (°)
C1AC2AC3
C2AC1AC7
C2AC3AC4
C3AC4AC5
C4AC5AC6
C6AC1AC7
C6AC1AC2
C1AC6AC5
N1AC7AC1
N1AC7AC8
C1AC7AC8
C9AN1AC7
N1AC9AC10
N1AC9AC11
C10AC9AC11
C9AC10AN2
C12AC11AC16
C12AC11AC9
C16AC11AC9
C11AC12AC13
C12AC13AC14
C13AC14AC15
C14AC15AC16
C11AC16AC15
C10AN2AO1
121.1(19)
120.8(14)
120.6(19)
119.6(2)
120.8
119.8
120.1
119.5
120.3
121.4
118.7
120.5
109.7
107.8
111.3
121.8
114.9
126.6
118.4
120.9
119.2
120.5
120.3
120.4
120.2
119.7
120.2
120.4
111.3
119.6(2)
121.3(13)
117.8(15)
121.1(19)
109.6(11)
106.6(12)
114.7(11)
121.1(10)
117.0(10)
125.1(11)
117.9(10)
118.9(10)
119.3(12)
120.9(12)
119.9(12)
120.5(16)
120.1(18)
120.3(15)
120.0(17)
119.9(16)
111.4(10)
13C NMR spectrum shows 9 different carbon atoms. The signal
at 164.27 ppm belongs to the C9 carbon atom and was calculated
at 172.69 ppm. The carbon resonance of the C@NAOH group occurs
at 152.63 ppm as expected for imine oximes [61,62] and was calcu-
lated as 162.89 ppm. The signals between 128.72 and 145.13 ppm
are assigned to both phenyl carbon atoms and compare well with
the calculated values. The C7 and C8 resonances are observed at
60.74 and 24.63 ppm, respectively and were calculated at 69.87
and 27.67 ppm, respectively.
3.6. UV–vis and photoluminescence spectra
Electronic absorption spectrum of compound I was studied in
EtOH using the TD-DFT. Singlet excited states were calculated to
predict the transition energies. The electronic transitions, oscillator
strengths and their assignments are given in Table 7. The title com-
pound displays a main absorption band centered at 236 nm
3.4. Vibrational spectra
Table 5 lists the experimentally observed FTIR bands of com-
pound I and the most intense vibrational frequencies calculated
by the DFT method at the B3LYP/6-311++G(d,p) level together with
their main mode contributions. The calculated frequencies with the
intensity less than 5 were not taken into consideration. The vibra-
tions below ca. 1450 cmÀ1 are very complex and involve several
coupled motions. In general, comparison of the experimental IR
bands and those obtained by the DFT method shows overall good
agreement as evident from inspection of Table 5. The band centered
at 3241 cmÀ1 corresponds to the vibration of the hydroxyl group,
which participates to strong hydrogen bonding in the crystalline
state as discussed above. The hydrogen bonding is important for
the stabilization of oximes [58] and the calculations showed that a
hydrogen bonded dimer of the title compound has lower energy
(À29.5 kJ molÀ1) compared to the single molecule. In the present
case, the difference between the experimental and calculated values
is 420 cmÀ1. The calculated aromatic and aliphatic CAH vibrations
were found in the range of 3060–2890 cmÀ1, in agreement with
(e
= 32,100 dm3 molÀ1 cmÀ1). However, the calculated spectrum
shows two absorption bands at 235 and 276 nm. The latter was
not observed experimentally. The assignment of the calculated
orbital excitations to the experimental bands was based on an
overview of the contour plots and relative energy of occupied
(HOMO) and unoccupied (LUMO) molecular orbitals involved in
the electronic transitions (Fig. 4). The HOMO orbital is mainly lo-
cated on one of the phenyl side, while the HOMO-4 orbital is local-
ized on the C@N and OH groups as well as one of the phenyl ring.
The LUMO orbital lies on the C@N and OH groups. The HOMO and
LUMO orbitals have a
band at 236 nm can be ascribed to the
p
character and the experimental absorption
p
?
pà transition between
HOMO-4 and LUMO at 235 nm with an oscillator strength of 0.72.
The title compound is fluorescent in DMSO solutions upon
excitation at room temperature. The room temperature emission
spectra of I are presented in Fig. 5. When the title compound is ex-
cited at 298 nm, it fluoresces at 355 nm. On the other hand, the

Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
69
Fig. 2. The optimized geometries of all isomers of compound I.
Table 3
Calculated dihedral angles, energies and dipole moments of the isomers of compound I.
Isomers
Dihedral angles (N1@C9/C10@N2)
E (a.u.)
D
E (kJ/mol)
l (D)
s-trans
s-cis
s-cis
s-trans
s-cis
s-cis
E
Z
E
E
Z
E
Z
Z
E
E
E
Z
Z
Z
E
Z
À178.5
2.3
34.4
152.2
À77.0
87.8
À804.2077
À804.2074
À804.2007
À804.1971
À804.1962
À804.1961
À804.1933
À804.1930
0.000
0.786
1.9123
5.5861
2.0893
1.2855
2.8763
0.9201
4.9202
0.9298
18.375
27.826
30.188
30.451
37.741
38.557
s-trans
s-trans
À167.9
À118.4
Table 4
Atomic charges of I.a
Table 5
Experimental and calculated IR spectral dataa of I together with their assignment.b
Atom
NBO
Assignment Experimental B3LYP/6-311++G(d,p)
(cmÀ1
)
C1
C2
C3
C4
C5
C6
C7
C8
À0.029
À0.196
À0.196
À0.208
À0.199
À0.204
À0.067
À0.556
0.231
Unscaled Scaled Intensity
m
m
m
m
m
m
m
m
m
m
m
m
m
(OAH)
3241m
3084m
3051w
3040w
3026m
3823
3194
3192
3184
3172
3125
3110
3099
3030
3021
1683
1666
1642
1524
1487
1482
1428
1387
3662 150
(CAH)ring1
(CAH)ring2
(CAH)ring1
(CAH)ring2
(CAH)CHNOH
(CAH)CH3 asym.,
(CAH)CH3 asym.
(CAH)CH3 sym.
(CAH)NCHCH3
(C@N)
3060
3058
3050
3039
2994
2979
2969
2903
2894
1646
1629
1606
1490
1454
1449
1397
1356
12
7
26
23
6
16
34
26
18
7
91
8
13
6
7
64
22
2974m
C9
m
(CAH)NCHCH3 2931w
C10
C11
C12
C13
C14
C15
C16
N1
N2
O1
0.033
À0.101
À0.176
À0.196
À0.199
À0.197
À0.188
À0.424
À0.122
À0.548
2898m
2872m
1612s
1597s
(C@N)
(C@C)ring1
d(CAH)ring2
1494s
1445w
1420w
1374w
1320w
c
c
(CAH)CH3
(CAH)CH3, d(CAH)ring1
,
d(OAH), d(CAH)CHNOH
d(CAH)ring2 (CAH)NCHCH3
r(CAH)CH3
d(CAH)ring2 (CAH)NCHCH3
r(CAH)CH3
,
c
,
,
a
Atomic charge units.
q
,
c
1303m
1357
1327
10
q
excitation at 378 nm gives an emission band with three maximum
at 439 nm. This band contains two maxima with a low intensity at
(continued on next page)

70
Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
Table 6
Table 5 (continued)
Experimental and calculated 1H and 13C NMR chemical shifts (ppm).a
Assignment
Experimental B3LYP/6-311++G(d,p)
(cmÀ1
Atom
Experimental
B3LYP/6-311++G(d,p)
)
Unscaled Scaled Intensity
1H NMR
O1AH
C10AH
C13AH
C14AH
C15AH
C12AH
C16AH
C3AH
C4AH
C5AH
C2AH
C6AH
c
(CAH)NCHCH3
d(CAH)ring2, d(OAH)
,
c
(CAH)CH3
,
1273m
1312
1283
8
11.79 s
7.88 s
7.44–7.26 m
8.09
8.39
7.79
7.77
7.72
7.52
7.15
7.61
7.60
7.91
7.00
d(OAH), d(CAH)CHNOH
d(OAH), d(CAH)CHNOH
d(CAH)ring1,2
1266
1117
1238
1092
54
19
,
m
(CAC),
1069m
1022s
m(NAO),
m(CAC),
m(CAN),
1020
998
33
d(C@C)ring1
r(CAH)CH3, d(C@C)ring1,2
r(CAH)CH3, d(CAH)ring1,2
q
q
1002
991
979
911
980
969
957
891
7
171
10
7.22–7.10 m
, m(NAO) 999s
c
q
(CAH)CHNOH
r(CAH)CH3
(CAH)ring2
918m
898m
,
c
(CAH)ring1
,
17
c
8.42
4.25
0.93–1.62
c(CAH)ring1
782w
755w
704m
821
788
758
803
771
741
12
5
8
C7AH
C8AH
4.45 m
1.32 d
c(CAH)ring2
q
r(CAH)CH3
,
13C NMR
C9
C10
C1
C11
C12
C5
C16
C14
C6
c(CAH)CHNOH,d(C@C)ring1,2
164.27
152.63
145.13
135.11
128.80
127.81
128.80
126.93
128.72
127.81
127.68
127.68
126.93
128.72
60.74
172.69
162.89
153.89
143.10
134.02
133.72
133.44
133.33
133.33
133.26
133.01
132.47
132.02
131.77
69.87
c(CAH)ring2
c(CAH)ring1
c(CAH)ring2
c(CAH)ring1
695s
684s
719
713
712
694
621
581
558
502
443
703
697
696
679
607
568
546
491
433
15
100
13
24
11
17
21
5
112
679w
669w
573m
540w
523vw
489vw
406w
d(C@C)ring2, d(C@C)ring1
d(C@C)ring2, d(C@C)ring1
c
c
(C@C)ring2
(C@C)ring1
q
r(OAH)
C3
a
w = weak, vw = very weak, s = strong, m = medium.
m
m = anti-symmetric, sym = symmetric, ring1 = C1AC6, ring2 = C11AC16.
C13
C15
C4
C2
C7
b
= streching, d = in-plane bending, c = out-of-plane bending, qr = rocking, asy-
C8
24.63
27.67
a
In DMSO-d6 with TMS as a reference.
Table 7
Experimental and calculated electronic transitions, oscillator strengths and their
assignments for compound I.a
Major contribution Character Calculated
Experimental
E (eV), e
k (nm), E (eV), fos k (nm),
D
D
Absorption
H-4 ? L (36%)
H ? L (74%)
p
p
?
?
pÃ
pÃ
235 5.29 0.72 236
276 4.50 0.03
5.26 32,100
À
Emission
H-8b ? Lb (61%)
Ha ? La (78%)
p
p
?
?
pÃ
pÃ
339 3.66 0.13 355b 3.50
443 2.80 0.08 439c 2.83
À
À
a
e
= Molar absorption coefficient (dm3 molÀ1 cmÀ1), fos = oscillator strength,
H = highest occupied molecular orbital, L = lowest unoccupied molecular orbital.
b
Excited at 298 nm.
Excited at 378 nm.
c
416 and 464 nm. Again,
in the transitions of the emission spectra have
The emissions observed at 355 and 439 nm are related to the trip-
let state HOMO-8(b) ? LUMO(b) and HOMO( ) ? LUMO( ) transi-
tions at 339 and 443 nm, respectively (Table 7). The energies of
a
- and b-spin molecular orbitals involved
p
character (Fig. 4).
a
a
both emissions are in good agreement with the
of the calculated spectra.
p–
pà transitions
4. Conclusions
(1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime is syn-
thesized and characterized by elemental analysis, UV–vis, IR, 1H
NMR, 13C NMR and X-ray diffraction. Molecular geometries, elec-
tronic structures, vibrational and NMR, spectra of the title com-
pound were investigated using the DFT method. The TD-DFT
calculations in the solution (EtOH and DMSO) were used to predict
Fig. 3. Experimental and calculated NMR spectra of compound I.

Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
71
Fig. 4. The molecular orbitals involved in the electronic transitions. The a- and b-spin HOMO and LUMO orbitals indicate the triplet state of I.
the nature of the electronic transitions observed in the absorption
and emission spectra. The calculated geometry of the s-trans-E,E
isomer is in good agreement with the X-ray crystallographic data
and the calculated vibrational spectra and chemical shift values
compare well with the experimental data. The calculated vibra-
tional bands and NMR chemical shifts are consistent with the
experimental results. The electronic absorption and emission spec-
tra calculated using the TD-DFT method were correlated to the
experimental spectra, and the assignment and analysis of the elec-
tronic transitions were performed using the frontier molecular
orbitals. The absorption band is consistent with the calculated
band within only 1 nm wavelength shift, while the calculated
Fig. 5. Experimental and calculated emission spectra of compound I.

72
Y. Kaya et al. / Journal of Molecular Structure 1024 (2012) 65–72
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