Synthesis, spectral, SHG efficiency and computational studies of some newly synthesized unsymmetrical azines of 4-biphenylcarboxaldehyde

Article abstract of DOI:10.1016/j.saa.2014.03.093

A series of novel unsymmetrical azines 2-8 are prepared and characterized by FT-IR, ¹H, ¹³C NMR, Mass and UV spectral studies. The Gaussian-03 B3LYP/6-311+G(d,p) calculations on these azines are used to evaluate the heat of formation of the different conformers, identify the stable conformation, to determine dipole moment (μ), polarizability (α₀), first hyperpolarizability (β_tot), selected geometrical parameters, MEP surface, frontier molecular orbital energies (HOMO-LUMO) and their energy gap. The μ, α₀, β_tot values clearly depict that the unsymmetrical azine 8 is found to have a good NLO property compared to other azines 1-7. The SHG measurement of unsymmetrical azine 8 was performed by Kurtz and Perry powder method and the results indicated that the azine 8 is having comparable efficiency as that of potassium dihydrogen phosphate (KDP) crystal. The natural bond orbital (NBO) analysis of the unsymmetrical azines 2-8 are also made using B3LYP/6-31G(d,p) basis set.

Full text of DOI:10.1016/j.saa.2014.03.093

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral, SHG efficiency and computational studies of some
newly synthesized unsymmetrical azines of 4-biphenylcarboxaldehyde
⇑
R. Arulmani, K.R. Sankaran
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
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
ꢀ
ꢀ
ꢀ
A series of novel unsymmetrical
azines 2–8 were synthesized and
analyzed by some spectral studies.
Hyperpolarizability, dipole moment,
HOMO–LUMO energies were
computed.
Computed IR frequencies are
compared with the observed values.
a r t i c l e i n f o
a b s t r a c t
A series of novel unsymmetrical azines 2–8 are prepared and characterized by FT-IR, 1H, 13C NMR, Mass
and UV spectral studies. The Gaussian-03 B3LYP/6-311+G(d,p) calculations on these azines are used to
evaluate the heat of formation of the different conformers, identify the stable conformation, to determine
Article history:
Received 26 October 2013
Received in revised form 28 February 2014
Accepted 18 March 2014
dipole moment (
l
), polarizability (
a
0), first hyperpolarizability (btot), selected geometrical parameters,
0, btot val-
Available online 1 April 2014
MEP surface, frontier molecular orbital energies (HOMO–LUMO) and their energy gap. The
l, a
ues clearly depict that the unsymmetrical azine 8 is found to have a good NLO property compared to
other azines 1–7. The SHG measurement of unsymmetrical azine 8 was performed by Kurtz and Perry
powder method and the results indicated that the azine 8 is having comparable efficiency as that of
potassium dihydrogen phosphate (KDP) crystal. The natural bond orbital (NBO) analysis of the unsym-
metrical azines 2–8 are also made using B3LYP/6-31G(d,p) basis set.
Keywords:
Unsymmetrical azines
HOMO–LUMO
NBO
Hyperpolarizability
NLO
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
p-conjugated backbone behave as novel nonlinear optical (NLO)
materials. This property of azine is attributed to the development
Azines, condensation products of hydrazine and carbonyl com-
pounds are designated as symmetrical or asymmetrical azines,
based on the two carbonyl compounds from which the azine
derived are the same or different. Azines are both chemically and
biologically important molecules with potent physical properties
[1–9]. Azines with donor and acceptor groups at the ends of
of light based technologies for communication and computing
[10]. Organic molecules with conjugated
p-electron system are
known to exhibit extremely large optical nonlinear responses in
terms of their molecular hyperpolarizabilities, with application in
many current areas of interest, such as second harmonic generator
(SHG) and linear-electro optimization (LEO) [11–13]. Only a lim-
ited work has been reported in the synthesis and biological aspects
of azines derived from several hetero aromatic and bicyclic car-
bonyl compounds. The present investigation is focussed on the
⇑
Corresponding author. Tel.: +91 4144 238601; fax: +91 4144 238145.
E-mail address: profkrs15@gmail.com (K.R. Sankaran).
http://dx.doi.org/10.1016/j.saa.2014.03.093
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

492
R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
synthesis and theoretical investigation of the molecular structures
and their NBO analysis of newly synthesized azines derived from
4-biphenylcarboxaldehyde having extended conjugation. HOMO–
LUMO energies, dipole moments, polarizabilities and first hyperpo-
larizabilities were determined by density functional theory (DFT)
method. SHG efficiency of unsymmetrical azine 8 was determined
by Kurtz and Perry powder technique.
ppm): d = 162.14 (C11); 161.83 (C21); 127.19–143.99 (aromatic
carbons). HRMS (m/z): 284.13. UV–Vis (DMF, nm): kmax = 325.5.
(1E,2E)-1-(4-methylbenzylidene)-2(biphenyl-4-ylmethylidene)
hydrazine 3
Yield 70%; m.p. 186 °C; yellow powder; molecular formula:
C
21H18N2. FT-IR (KBr, cmꢁ1): 3029 (CH stretching); 1620 (CH@N).
1H NMR (500 MHz, CDCl3, ppm): d = 8.74 (s, CH, 11H); 8.70 (s,
CH, 21H), 7.30–7.95 (aromatic protons). 13C NMR (125 MHz, CDCl3,
ppm): d = 162.20 (C11); 161.43 (C21); 127.16–143.85 (aromatic
carbons). HRMS (m/z): 298.15. UV–Vis (DMF, nm): kmax = 326.0.
Experimental details
Materials
(1E,2E)-1-(4-methoxybenzylidene)-2(biphenyl-4-y1methylidene)
hydrazine 4
4-Biphenylcarboxaldehyde was purchased from Sigma–Aldrich
and is used as such. All the reagents and solvents were of labora-
tory grade.
Yield 70%; m.p. 144 °C; yellow powder; molecular formula:
C
21H18N2O1. FT-IR (KBr, cmꢁ1): 3060 (CH stretching); 1617
(CH@N). 1H NMR (500 MHz, CDCl3, ppm): d = 8.73 (s, CH, 11H);
8.68 (s, CH, 21H); 7.01–7.94 (aromatic protons). 13C NMR
(125 MHz, CDCl3, ppm): d = 162.82 (C11); 161.07 (C21); 114.31–
162.19 (aromatic carbons). HRMS (m/z): 314.14. UV–Vis (DMF,
nm): kmax = 333.5.
Methods
All the melting points were performed in open capillary tube
melting point apparatus and are uncorrected. The IR spectra were
recorded in potassium bromide (KBr) disk on a Nicolet Avatar 360
FT-IR spectrometer and the wave numbers are given in cmꢁ1. The
1H and 13C NMR and 2D NMR spectra were recorded at 400, 500
and 100, 125 MHz on a Bruker spectrometer in CDCl3, TMS was used
as an internal standard and the chemical shift values (d) are given in
parts per million (ppm). The Mass spectra were performed using
Varian Saturn 2200 GC–MS spectrometer. The UV–visible spectra
of the azines are recorded in Shimadzu UV-1800 UV–visible
spectrophotometer using N,N-dimethylformamide as solvent at
ambient room temperature.
(1E,2E)-1-(4-chlorobenzylidene)-2(biphenyl-4-y1methylidene)
hydrazine 5
Yield 70%; m.p. 170 °C; yellow powder; molecular formula:
C
20H15ClN2. FT-IR (KBr, cmꢁ1): 3057 (CH stretching); 1620 (CH@N).
1H NMR (500 MHz, CDCl3, ppm): d = 8.72 (s, CH, 11H); 8.67 (s, CH,
21H); 7.42–7.95 (aromatic protons). 13C NMR (125 MHz, CDCl3,
ppm): d = 162.11 (C11); 160.70 (C21); 127.16–144.10 (aromatic
carbons). HRMS (m/z): 318.09. UV–Vis (DMF, nm): kmax = 325.5.
(1E,2E)-1-(4-bromobenzylidene)-2(biphenyl-4-y1methylidene)
hydrazine 6
NLO technique
Yield 70%; m.p. 174 °C; pale yellow powder; molecular formula:
C
20H15BrN2. FT-IR (KBr, cmꢁ1): 3057 (CH stretching); 1621 (CH@N).
In order to confirm the second order nonliner optical properties
of the material, the second harmonic generation (SHG) test on the
powder sample of a representative azine 8 was performed by Kurtz
and Perry powder SHG method [14]. A Q-switched Nd:YAG laser
wavelength 1064 nm was used with input radiation 2.2 mJ/pulse.
A small portion of the azine 8 was powdered to a uniform particle
size of about 125–150 nm and then packed in a capillary of uni-
form bore and exposed to laser radiations. The output from the
sample was monochromated to collect only the second harmonic
(532 nm) and the intensity was measured using a photomultiplier
tube.
1H NMR (500 MHz, CDCl3, ppm): d = 8.72 (s, CH, 11H); 8.66 (s, CH,
21H); 7.17–7.95 (aromatic protons). 13C NMR (125 MHz, CDCl3,
ppm): d = 162.14 (C11); 160.79 (C21); 125.66–144.12 (aromatic
carbons). HRMS (m/z): 362.04. UV–Vis (DMF, nm): kmax = 328.5.
(1E,2E)-1-(4-fluorobenzylidene)-2(biphenyl-4-y1methylidene)
hydrazine 7
Yield 70%; m.p. 164 °C; pale yellow powder; molecular formula:
C
20H15FN2. FT-IR (KBr, cmꢁ1): 3059 (CH stretching); 1624 (CH@N).
1H NMR (400 MHz, CDCl3, ppm): d = 8.67 (s, CH, 11H); 8.73 (s, CH,
21H); 7.15–7.93 (aromatic protons). 13C NMR (100 MHz, CDCl3,
ppm): d = 163.39 (C11); 160.92 (C21); 116.06–161.95 (aromatic
carbons). HRMS (m/z): 302.12. UV–Vis (DMF, nm): kmax = 328.0.
Synthesis of unsymmetrical azines 2–8
Synthesis of (1E,2E)-1-benzylidene-2(biphenyl-4-ylmethylidene)
hydrazine 2
(1E,2E)-1-(4-nitrobenzylidene)-2(biphenyl-4-y1methylidene)
hydrazine 8
About 0.01 mol of 4-biphenylcarboxaldehyde and 5 mL of
hydrazine hydrate (0.01 mol) was taken in a stoppered conical
flask. To this mixture few drops of acetic acid was added. The reac-
tion mixture was stirred well for about half an hour. The hydrazine
was separated as white solid and it was stirred with benzaldehyde
(0.005 mol). The mixture was cooled. Yellow solid separated out
and it was filtered, washed and recrystallized from ethanol. The
other unsymmetrical azines 3–8 are synthesized in the similar
manner. All the synthesized azines were characterized by FT-IR,
1H, 13C NMR, Mass and UV spectral analysis. The reaction pathway
has been summarized in Scheme 1.
Yield 70%; m.p. 198 °C; yellow solid; molecular formula:
C
20H15N3O2. FT-IR (KBr, cmꢁ1): 3060 (CH stretching); 1617
(CH@N). 1H NMR (500 MHz, CDCl3, ppm): 8.76 (s, CH, 11H); 8.75
(s, CH, 21H); 7.43–7.97 (aromatic protons). 13C NMR (125 MHz,
CDCl3, ppm): d = 162.11 (C11); 160.70 (C21); 124.07–161.83 (aro-
matic carbons). HRMS (m/z): 329.12. UV–Vis (DMF, nm):
kmax = 345.0.
Results and discussion
Yield 70%; m.p. 140 °C; yellow powder; molecular formula:
The FT-IR spectra and high resolution 1H and 13C NMR spectra
of (1E,2E)-1-benzylidene-2(biphenyl-4-y1methylidene)hydrazine
2, (1E,2E)-1-(4-methylbenzylidene)-2(biphenyl-4-y1methylidene)
C
20H16N2. FT-IR (KBr, cmꢁ1): 3050 (CH stretching); 1618 (CH@N).
1H NMR (400 MHz, CDCl3, ppm): d = 8.71 (s, CH, 11H), 8.70 (s,
CH, 21H); 7.38–7.48 (aromatic protons). 13C NMR (100 MHz, CDCl3,
hydrazine
3,
(1E,2E)-1-(4-methoxybenzylidene)-2(biphenyl-4-

R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
493
Scheme 1. Synthetic route of unsymmetrical azines 2–8.
y1methylidene)hydrazine 4, (1E,2E)-1-(4-chlorobenzylidene-2(biphe-
nyl-4-y1methylidene)-hydrazine 5, (1E,2E)-1-(4-bromobenzylidene-2
(biphenyl-4-y1methylidene)hydrazine 6, (1E,2E)-1-(4-fluorobenzylid-
ene)-2(biphenyl-4-y1methylidene)hydrazine 7 and (1E,2E)-1-(4-nitro-
7.92 ppm is assigned to the protons in the biphenyl ring i.e.,
H(13) and H(17). A doublet of doublet at 7.86 ppm (integral corre-
sponds to two protons) is assigned to the ortho protons of the ben-
zylidene ring [H(23) and H(27)]. The two doublets at 7.69 and
7.64 ppm are assigned to the protons in the biphenyl ring H(14)
and H(16) and H(152) and H(156), respectively. For the remaining
aromatic protons signals are observed in the range 7.38–7.48 ppm.
They were assigned to H(24), H(26); H(153), H(155) and H(154)
and H(25) based on the correlations observed in the 1H-1H COSY
spectrum. In a similar manner assignments were done for other
hydrazines 3–8. 1H–1H COSY spectra of 2 are shown in Fig. S3 (a
and b).
benzylidene)-2(biphenyl-4-y1methylidene)hydrazine
recorded and analyzed.
8 have been
Spectral studies
FT-IR spectral studies of 2–8
The sharp peaks around 1600 cmꢁ1 in the FT-IR spectra are
exhibited to vC@N mode. Aromatic C@C stretching vibrations are
seen around 1500 and 1450 cmꢁ1. The peaks around 1069–
1005 cmꢁ1 are due to the N–N stretching mode. Aromatic CAH
out-of-plane bending vibrations appeared around 840 and
13C NMR spectral studies of 2. The assignment of signals in the 13C
NMR spectrum of 2 is made as follows. The two high frequency sig-
nals at 162.14and 161.83 ppm are due to azomethine carbons
C(11) and C(21) respectively. The high intense signals at 128.62
and 128.84 ppm were due to ortho [C(23) and C(27)] and meta
[C(24) and C(26)] carbons of the benzylidene ring. The remaining
high intense signals at 129.08, 127.52, 127.19 and 128.91 ppm
were assigned to biphenyl ring carbons (ortho with respect to azo-
methine carbon C(11) i.e., C(13) and C(17); meta [C(14) and C(16)])
and remaining carbons C(152), C(156), C(153) and C(155), respec-
tively. These assignments were further confirmed from the correla-
tions observed in the 1H-13C COSY spectra of 2 are shown in Fig. S4
(a and b). The 13C NMR spectrum further reveals four signals for
quaternary carbons [C(12), C(22), C(15) and C(151)] at 133.05,
134.15, 143.99, 140.30, ppm which can easily be distinguished
from other carbons based on small intensities. The signals at
133.05 and 134.15 ppm are assigned to the ipso carbons C(12)
757 cmꢁ1
. Two very strong adsorption bands at 1515 and
1337 cmꢁ1 in the FT-IR spectrum of unsymmetrical azine 8 are
attributed to antisymmetric and symmetric NO2 stretching vibra-
tions respectively. Asymmetric bending vibration for methyl group
appeared at 1300 cmꢁ1 for azine 3. FT-IR spectral data of 2–8 are
listed in Table 1.
NMR spectral studies
1H NMR spectral analysis of unsymmetrical azine 2. The signals in
the 1H NMR spectra were assigned based on their positions inte-
grals and multiplicities and confirmed by the correlations observed
in the COSY spectra. 1H and 13C NMR spectra of 2 are shown in
Figs. S1 and S2.
Two high frequency singlets at 8.72 and 8.70 ppm were
assigned to the protons H(11) and H(21). A doublet observed at
Table 1
IR spectral data (cmꢁ1) of unsymmetrical azines 2–8.
Assignments
2
3
4
5
6
7
8
vC@N
1618
1620
1617
1620
1591
1484
1621
1585
1483
1402
1624
1599
1505
1228
1406
1153
1623
1599
1515
1485
vC@C
1483
1483
1410
1248
vNAN
1005
957
834
757
–
1175
1006
816
763
–
1170
1028
834
764
–
1089
1008
827
761
–
1069
1008
827
761
–
1185
1337
840
769
1515 1337
–
Aromatic CH out-of-plane bending vibration
833
761
–
vNO2
vCH3
–
1300
1303
–
–
–

494
R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
Table 2
1H chemical shifts (ppm) and coupling constants (Hz) of unsymmetrical azines 2–8.
Compds. H(21)
H(23) and H(27)
H(24) and
H(26)
H(11)
H(13) and
H(17)
H(14) and
H(16)
H(152) and
H(156)
H(153) and
H(155)
H(154) H(25) H(26)
2
3
4
5
6
7
8
8.70
(s)
8.70
(s)
8.68
(s)
8.67
(s)
8.66
(s)
8.73
(s)
8.75
(s)
7.86 (dd, 5.60,
7.20)
7.79 (d, 8.00)
7.47–7.48
8.72
(s)
8.74
(s)
8.73
(s)
8.72
(s)
8.72
(s)
8.67
(s)
8.76
(s)
7.92 (d, 8.50)
7.95 (d, 8.00)
7.94 (d, 8.50)
7.95 (d, 8.50)
7.95 (d, 8.00)
7.93
7.69 (d, 8.50)
7.72 (d, 8.50)
7.71 (d, 8.00)
7.72 (d, 8.00)
7.72 (d, 8.00)
7.71–7.68
7.64 (d, 7.50)
7.67 (d, 7.50)
7.67 (d, 7.50)
7.67 (d, 7.50)
7.17 (d, 7.00)
7.66–7.63
7.47–7.48
7.50 (t)
7.50
7.38
(t)
7.41
(t)
7.45
–
–
7.30 (d, 7.50)
7.01 (d, 8.50)
7.46 (d, 8.50)
7.62 (d, 8.50)
7.15
2.47
7.84 (d, 9.00)
7.82 (d, 8.50)
7.76 (d, 8.00)
7.87–7.82
7.41
–
3.90
(s)
–
7.50 (t)
7.50 (t)
7.48
7.42
(t)
7.42
(t)
7.39
(t)
7.43
(t)
–
–
–
–
–
–
8.05 (d, 8.50)
8.34 (d, 9.00)
7.97 (dd, 8.00) 7.73
7.68 (d, 7.50)
7.51 (d, 7.50)
–
Values within parentheses are observed coupling constants in Hz.
and C(22) and the remaining signals at 140.30 and 143.99 ppm are
assigned to C(151) and C(15), respectively. In a similar manner
assignments were made for other azines 3–8. The 1H and 13C
chemical shifts obtained in this manner were listed in Tables 2
and 3, respectively.
first hyperpolarizability (b) were calculated by finite field approach
using B3LYP/6-31Gꢂ basis set. Highest occupied molecular orbital
(HOMO), lowest unoccupied molecular orbital (LUMO) energies
and other thermodynamic properties of the stable conformer were
determined by DFT method.
Experimental and theoretical IR spectral analysis of 2
Electronic spectral studies
Many quantum chemical computations are used in vibrational
analysis of many compounds [16,17]. The IR frequencies of 2 were
determined theoretically by DFT using B3LYP/6-31G(d,p) method
and the data were displayed in Table 6 along with the observed
values. The vibrational frequencies obtained from the computa-
tional studies are scaled with proper factor for B3LYP/6-31G(d,p)
method i.e., 0.9679 [18]. There is a close agreement between the
calculated IR frequencies with the experimental ones.
The ultraviolet absorption spectra are recorded for all the newly
synthesized unsymmetrical azines in dimethylformamide in the
region 260–400 nm. The maximum absorption lays around 325.5,
326.0, 333.5, 325.5, 328.5, 328.0 and 345.0 nm for the azines 2–
8, respectively. All the absorption bands are due to the n-pꢂ transi-
tion. The higher kmax is observed for 8 when compared to other
unsymmetrical azines 2–7 due to the presence of nitro group in
8. UV–Vis spectrum of 2 is shown in Fig. S5.
NLO analysis
Computational studies
First polarizability can be described by a (3 ꢃ 3 ꢃ 3) matrix, the
27 components of the 3D matrix can be reduced to 10 components
due to their Kleinman symmetry [19]. The total static dipole
There are four possible conformations for the azine 2 and these
conformations are illustrated in Fig. 1. In order to decide the
favoured conformation computational calculations were performed
according to DFT method using B3LYP/6-311+G(d,p) basis set avail-
able in Gaussian-03 package [15]. The conformer in which heat of
formation is minimum is predicted to be the stable conformer and
the values of the conformers other than stable conformer are
reported as relative values with respect to the favoured conformer.
The relative heat of formations thus determined in this manner for
the unsymmetrical azines 2–8 were displayed in Table 4.
Among the four conformers of azines 2–8, the conformer A is
found to be the stable conformer. The structure of stable conformer
along with numbering of atoms adopted in this study is given in
Fig. 2. The bond lengths, bond angles and torsional angles of the
stable conformer of all the azines 2–8 are given in Table 5.
Further, vibrational frequencies are also computed using B3LYP/
moment (
polarizability (
are related directly to the nonlinear optical efficiency of structures.
The calculated values of 0, btot by finite field approach are given
l), the mean polarizability (
a0), the anisotropy of the
D
a
) and the mean first hyperpolarizability (btot
)
l, a
in Table 7 along the corresponding components using the x, y, z
components are defined as
l
¼ ðl2x
þ
ly2
þ
l2z Þ1=2
ð1Þ
2
2
2
D
a
¼ 2ꢁ1=2½ðaxx
ꢁ
ayyÞ þ ðayy
ꢁ
azzÞ þ ðazz
ꢁ
axxÞ þ 6
a
2xxꢄ1=2
ð2Þ
The
a
is a second rank tensor property called dipole polarizability,
i is evaluated using
6-31G(d,p). The total static dipole moments, polarizability (
a) and
the mean polarizability h
a
Table 3
13C Chemical shifts (ppm) of unsymmetrical azines 2–8.
Compds. C(11)
C(21)
C(12)
C(15)
C(151) C(22)
C(25)
C(17)
and
C(14)
and
C(152)
and
C(153)
and
C(154) C(23)
and
C(24)
and
C(26)
C(13)
C(16)
C(156)
C(155)
C(27)
C(26)
2
3
4
5
6
7
8
162.14 161.83 133.05 143.99 140.30 134.15 131.22 129.08
162.20 161.43 133.15 143.85 140.45 131.44 141.75 129.00
161.82 161.07 133.24 143.75 140.34 126.88 162.19 130.32
162.11 160.70 132.92 144.10 140.24 132.67 129.08 129.72
162.14 160.79 133.09 144.12 140.23 132.91 125.66 129.94
163.39 160.92 133.00 144.04 140.30 161.83 161.95 128.94
160.44 159.32 132.57 144.58 140.05 149.19 161.83 129.39
127.52
127.47
127.46
127.51
127.52
127.53
127.61
127.19
127.16
127.15
127.16
127.16
127.19
127.20
128.91
128.91
128.92
129.11
129.12
129.08
128.99
127.94 128.62
127.88 128.61
127.85 127.46
127.95 128.93
127.95 128.92
127.94 130.56
128.10 129.15
128.84
129.58
114.31
129.14
132.10
116.06
124.07
–
21.65
55.42
–
–
–
–

R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
495
Table 4
Relative heat of formation values (kJ molꢁ1) of various conformers for unsymmetrical
azines 2–8.
Compds.
Conformers
A
B
C
D
2
3
4
5
6
7
8
0
0
0
0
0
0
0
20.85
21.98
21.72
21.68
21.81
22.31
22.27
21.43
21.89
21.68
22.19
22.19
21.72
21.72
33.28
34.20
34.37
34.12
34.24
34.12
34.49
btot ¼ ðb2x þ by2 þ b2z Þ1=2
ð5Þ
The complete equation for calculating the magnitude of first
hyperpolarizability from GAUSSIAN-03W output is given as
follows:
1=2
2
2
2
btot ¼ ½ðbxxx þbxyy þbxzzÞ þðbyyy þbyzz þbyxxÞ þðbzzz þbzxx þbzyyÞ ꢄ
ð6Þ
To calculate all the electric dipole moments and the first hyper-
polarizabilities, the origin of the Cartesian coordinate system (x, y,
z) = (0, 0, 0) was chosen at own centre of mass of each compound.
The
l
values of 2–8 are 0.34, 0.40, 1.94, 2.64, 2.51, 1.90, 6.67
x) is
Debye, respectively. The highest value of dipole moment (
l
observed for 8 compared to other azines. The unsymmetrical
azines 2–8 are found to be polar molecules having non-zero dipole
moment values. These result in large microscopic first hyperpolar-
izabilties and hence have a good microscopic NLO behaviour.
The calculated polarizabilities aij have non-zero values and
dominated by the diagonal components (axx, ayy, azz). The b value
of components 2–8 indicate that the azine 8 which has electron-
withdrawing group (ANO2) is found to have greater molecular
asymmetry than all other azines. Delocalization of charges in par-
ticular direction is indicated by large values of those particular
components of polarizability and hyperpolarizability. Among the
azines, the azine 8 was found to have a good NLO behaviour that
is indicated by its high first hyperpolarizability value of
188 ꢂ 107 esu. The NLO behavioural analysis of azine 8 also has
been studied experimentally by SHG test. A second harmonic sig-
nal of 24 mV was obtained. The standard potassium dihydrogen
phosphate (KDP) crystal gave an SHG signal of 24.4 mV for the
same input energy. From the obtained results it was evident that
the relative SHG efficiency of sample was almost equal to that of
well known KDP crystal. From that it is clear that the azine 8 is
NLO active in nature.
Fig. 1. Possible conformations of azines 2–8.
1
3
h
ai ¼
ðaxx
þ
ayy
þ
azz
Þ
ð3Þ
The components of the first hyperpolarizability can be calcu-
lated using the following equation
X
1
3
bi ¼ biii
þ
ðbijj þ bjij þ bjjiÞ
ð4Þ
HOMO–LUMO energies
i–j
The NLO response can be qualitatively understood by
examining the energetics of frontier molecular orbital
(HOMO–LUMO) of azines 2–8 (Table 8).
Using the x, y and z components the magnitude of the first
hyperpolarizabilty tensor can be calculated by
Fig. 2. Optimized geometry of the most favourable conformation of 2 along with numbering.

496
R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
Table 5
Selected geometric parameters [bond lengths (Å), bond angles (°) and torsional angles (°)] in unsymmetrical azines 2–8 by DFT/B3LYP/6-31G(d,p) method.
Geometric parameters
Compounds
2
3
4
5
6
7
8
Bond length
C17AC12
C13AC12
C12AC11
C11AN1
1.40
1.41
1.46
1.28
1.39
1.28
1.46
1.40
1.41
1.39
1.39
1.40
1.39
–
1.40
1.40
1.46
1.28
1.39
1.28
1.46
1.40
1.41
1.39
1.40
1.40
1.38
1.51
1.40
1.40
1.46
1.28
1.39
1.29
1.46
1.40
1.41
1.39
1.40
1.41
1.38
1.36
1.40
1.40
1.46
1.28
1.39
1.28
1.46
1.40
1.40
1.39
1.39
1.39
1.39
1.34
1.40
1.40
1.46
1.28
1.39
1.28
1.46
1.40
1.40
1.39
1.39
1.40
1.40
1.92
1.40
1.40
1.46
1.28
1.39
1.28
1.46
1.40
1.41
1.39
1.39
1.39
1.39
1.35
1.40
1.41
1.46
1.29
1.39
1.28
1.46
1.40
1.41
1.39
1.39
1.39
1.38
1.48
N1AN2
C21AN2
C21AC22
C22AC23
C22AC27
C23AC24
C24AC25
C25AC26
C26AC27
C25AX28
Bond angle
C17AC12AC11
C13AC12AC11
C11AN1AN2
N2AC21AC22
C22AC23AC24
C24AC25AC26
C25AC26AC27
C22AC27AC26
C26AC25AX28
119.3
122.3
112.7
122.6
120.2
119.9
119.9
120.7
–
119.5
122.1
112.6
122.5
120.4
118.1
120.9
120.8
120.1
119.5
122.2
112.7
122.6
120.8
119.7
119.4
121.6
124.6
122.1
119.5
112.5
122.2
121.1
121.3
119.3
120.8
119.4
119.5
122.1
112.4
122.2
120.8
121.3
118.9
121.1
119.4
119.5
122.1
112.5
122.4
120.7
122.2
118.4
121.1
118.9
119.4
122.1
112.3
121.8
120.5
122.0
118.5
120.5
118.9
Torsional angle
C17AC12AC11AN1
C11AN1AN2AC21
C13AC12AC11AN1
N2AC21AC22AC27
C22AC23AC24AC25
C23AC24AC25AC26
C24AC25AC26AC27
C23AC24AC25AX28
C27AC26AC25AX28
C25
0.0
179.7
179.7
ꢁ0.2
180.0
ꢁ0.1
0.1
ꢁ0.1
ꢁ179.5
179.5
1.5
179.6
179.4
ꢁ0.4
179.7
ꢁ0.0
ꢁ0.0
0.0
ꢁ180.0
ꢁ180.0
1.4
179.7
179.5
ꢁ0.1
179.7
179.7
ꢁ0.2
179.8
ꢁ0.0
0.0
ꢁ0.0
ꢁ179.9
180.0
1.9
179.7
179.6
ꢁ0.2
179.9
ꢁ0.0
0.0
ꢁ0.0
ꢁ180.0
180.0
1.3
179.8
179.7
ꢁ0.2
179.6
ꢁ0.4
179.8
ꢁ0.0
0.0
0.0
–
–
–
179.8
ꢁ0.0
179.9
ꢁ0.0
ꢁ0.0
ꢁ0.0
ꢁ0.0
ꢁ0.0
ꢁ180.0
ꢁ180.0
1.2
ꢁ180.0
ꢁ180.0
1.5
X = CH3, OCH3, Cl, Br, F, NO2.
From the HOMO–LUMO analysis it is clear that the intramolec-
ular charge transfer (ICT) must occur within the molecule. The
HOMO–LUMO energy gap of azine 2 is relatively higher than that
of azines 3–8. This shows the lower btot value of azine 2 than those
of azines 3–8. It is evident that there should be an inverse
relationship between HOMO–LUMO energy gap and the first order
hyperpolarizability [20]. This fact is supported by UV–visible spec-
tral study which visualizes a large kmax for azine 8 which has lower
energy gap. The HOMO pictures of all the azines except the azine 8
reveal that all atoms get involved in the formation of the HOMO
orbitals. In nitro substituted benzylidene hydrazine 8, the pz orbi-
tals of C(24) and C(26) are not participated, however the pz orbitals
of nitro group are well participated in the formation of HOMO
orbitals.
In benzylidene hydrazines 2, 6 and 7, all the pz orbitals mainly
from the biphenyl ring atoms and side chain atoms are involved in
the formation of LUMO orbitals except pz orbitals of carbon atoms
C(155) and C(153). In azines 3 and 4, the pz orbitals of carbon
atoms C(155), C(153), C(24) and C(26) are not involved in the for-
mation of LUMO orbitals. In nitro substituted benzylidene hydra-
zine 8, the pz orbitals of carbon atoms C(155), C(154), C(153),
C(152), C(156), C(151), C(16) and C(14) are not involved in the
formation of LUMO orbital. The HOMO–LUMO pictures of the azine
2 is given in Fig. S6.
Table 6
Experimental and computed [B3LYP/6-31G(d,p) method] vibrational frequencies of
unsymmetrical azine 2.
Observed vibrational
Calculated vibrational frequency (cmꢁ1
(correction factor: 0.9679)
)
IR
frequency (cmꢁ1
)
intensity
3050.08
2933.01
1667.15
1618.56
1483.25
1444.25
1301.38
1214.04
1005.20
957.99
2999.76
3105.55
1621.45
1660.64
1550.98
1485.09
1295.14
1208.76
992.18
847.08
752.75
686.89
679.55
37.90
24.01
27.26
275.23
14.03
25.64
28.46
22.83
10.03
12.22
13.92
24.31
25.80
NBO analysis
NBO analysis have been performed on the molecules at the DFT/
B3LYP/6-31G(d,p) level in order to elucidate the intermolecular,
rehybridization and delocalization of electron density within the
molecule. The second order Fock matrix was carried out to evalu-
ate the donor–acceptor interactions in the NBO analysis and the
values are displayed in Table 9. The interactions result is a loss of
occupancy from the localized NBO of the idealized Lewis structure
into an empty non-Lewis orbital. For each donor (i) and acceptor
(j), the stabilization energy E(2) associated with the delocalization
i ? j is estimated as
834.57
757.36
690.38

R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
497
Table 7
The electric dipole moment
method.
l
(D), the mean polarizability h
a
i (ꢃ10ꢁ24 esu) and the first hyperpolarizability btot (ꢃ10ꢁ33 esu) of unsymmetrical azines 2–8 by B3LYP/6-31Gꢂ
2
3
4
5
6
7
8
axx
axy
ayy
axz
ayz
azz
83.89
89.215
90.708
92.157
95.461
84.852
ꢁ1.5954
30.330
91.959
ꢁ1.661
30.383
ꢁ0.1062
0.037
12.771
42.346
21151.69
1058.521
9.875
121.121
ꢁ33.666
ꢁ348.413
ꢁ79.831
ꢁ169.336
27.469
ꢁ3.044
22
ꢁ1.324
ꢁ1.898
ꢁ1.0403
ꢁ0.822
ꢁ2.1680
31.475
31.599
30.893
31.506
31.117
ꢁ0.06815
0.0969
14.137
ꢁ1.6318
0.1777
14.775
ꢁ0.2167
0.0724
13.462
ꢁ0.2560
0.1032
14.235
ꢁ0.1180
ꢁ0.0051
0.5410
16.086
0.0763
12.913
42.70
ha
i
44.94
45.69
45.504
47.07
46.39
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
5260.812
564.819
198.337
47.358
ꢁ100.527
ꢁ311.354
ꢁ100.527
93.239
9854.304
928.171
175.596
ꢁ164.721
ꢁ82.382
ꢁ264.445
ꢁ82.382
160.066
ꢁ7.438
ꢁ388.759
5.2
23575.36
442.0606
ꢁ107.042
ꢁ48.839
ꢁ93.564
ꢁ328.324
ꢁ59.613
ꢁ139.33
ꢁ15.918
11.951
20726.51
384.175
ꢁ225.932
ꢁ79.262
105.577
ꢁ291.957
ꢁ18.448
ꢁ81.7465
36.402
15279.32
740.200
276.019
ꢁ53.111
18.016
ꢁ383.168
ꢁ64.369
ꢁ103.334
ꢁ23.31
1.1161
11
61939.95
1087.504
ꢁ351.931
137.822
ꢁ9.464
ꢁ263.825
ꢁ76.310
ꢁ188.27
ꢁ3.09043
13.998
byzz
bzzz
btotalꢂ107
140.600
85.854
1.5
ꢁ13.050
27.2
20
188
a
= 1 a.u = 0.1482 ꢂ 10ꢁ24 esu.
b = 1 a.u = 8.6393 ꢂ 10ꢁ33 esu.
electron donors and electron acceptors, i.e., the more donating ten-
dency from electron donors to electron acceptors and the greater
the extent of charge transfer or conjugation of the whole system.
From Table 9, it is seen that the primary delocalization occurs
from the biphenyl ring to benzylidene ring only rather than vice
versa. Delocalization energy corresponding to the transfer of elec-
trons from bonding orbital of N2AC21 bond to the antibonding
orbital of N1AC11 (ꢅ57 kJ molꢁ1) is higher when compared to
reverse transfer (ꢅ50 kJ molꢁ1). Therefore electrons flow occurs
from biphenyl ring to the benzene ring side.
Table 8
HOMO–LUMO energies (eV) and dipole moments
l
(D) of unsymmetrical azines 2–8.
Compds.
HOMO–LUMO energies
Dipole moment
HOMO
LUMO
Energy gap (
D
E)
ltot
2
3
4
5
6
7
8
ꢁ0.224
ꢁ0.218
ꢁ5.714
ꢁ0.224
ꢁ0.224
ꢁ0.222
ꢁ0.234
ꢁ0.084
ꢁ0.078
ꢁ2.0136
ꢁ0.086
ꢁ0.086
ꢁ0.082
ꢁ0.111
3.81
3.81
3.70
3.75
3.75
3.81
3.35
0.35
0.41
1.94
2.64
2.52
1.91
6.68
The energy (E(2)) due to the transfer of electron from bonding
orbital C15AC16 to antibonding orbital C12AC17 is found to be
very high (E(2) = 93 kJ molꢁ1). The highest interaction is ꢁfo1und in
the azine 8 which has highest E(2) value of 95.29 kJ mol
.
2
Fði; jÞ
Eð2Þ ¼
D
Eij ¼ qi
ð7Þ
j are diagonal ele-
e
i ꢁ
ej
Thermodynamic properties
where qi is the donor orbital occupancy,
ments and F(i,j) is the off diagonal NBO Fock matrix element. The
larger the E(2) value, the more intensive is the interaction between
e
i and
e
Thermodynamic parameters have been calculated by using DFT
method at B3LYP/6-31G(d,p) level [21] and the parameters are
given in Table 10.
Table 9
Delocalization energies (E(2), kJ molꢁ1) for unsymmetrical azines 2–8 by NBO analysis.
Donor
Acceptor
2
3
4
5
6
7
8
N1AC11
N2AC21
N2AC21
N1AC11
N1AC11
C13AC14
C15AC16
N2AC21
54.88
54.63
80.76
79.42
81.51
79.88
79.42
81.81
77.49
86.28
93.57
72.38
81.47
87.79
87.79
83.90
84.65
85.36
80.51
87.71
87.67
76.70
54.17
55.14
80.30
83.52
81.93
81.85
81.76
75.90
77.58
86.12
93.15
72.51
81.47
87.96
84.44
83.86
84.48
85.36
76.95
94.16
94.16
72.38
54.76
54.59
80.80
79.38
81.55
80.38
82.27
81.34
86.20
86.20
93.53
72.43
81.47
20.97
20.16
83.86
20.22
20.39
76.95
93.70
89.43
73.31
55.89
53.67
81.72
79.46
80.88
78.04
80.30
92.90
77.41
86.45
93.86
72.18
81.47
87.50
84.44
83.94
84.90
76.91
78.37
86.70
78.46
74.98
55.89
50.24
81.85
79.38
80.80
78.00
79.84
93.61
77.37
86.08
94.37
72.38
81.47
87.79
84.36
83.98
84.61
85.24
78.75
85.41
77.95
75.48
55.09
54.21
81.14
79.38
81.30
79.96
85.45
83.35
77.49
86.28
93.82
72.34
81.47
87.67
84.44
83.90
84.78
87.08
73.31
93.78
88.04
71.30
57.48
52.50
82.98
79.46
80.00
74.23
79.00
95.96
77.28
86.75
95.29
71.81
81.43
87.08
84.44
84.02
85.28
85.20
81.09
88.34
76.49
80.05
C12AC17
C12AC17
C12AC17
C22AC27
C22AC27
C22AC27
C13AC14
C13AC14
C15AC16
C15AC16
C151AC156
C151AC156
C152AC153
C152AC153
C154AC155
C154AC155
C23AC24
C23AC24
C25AC26
C25AC26
C23AC24
C25AC26
C12AC17
C15AC16
C12AC17
C13AC14
C152AC153
C154AC155
C151AC156
C154AC155
C151AC156
C152AC153
C22AC27
C25AC26
C22AC27
C23AC24

498
R. Arulmani, K.R. Sankaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 491–498
Table 10
Theoretically calculated thermodynamic properties of unsymmetrical azines 2–8.
Parameters
2
3
4
5
6
7
8
Total energy
ꢁ880.96
192.007
1.666
ꢁ920.251
209.407
1.644
ꢁ995.444
212.200
1.535
ꢁ1340.564
185.903
1.654
ꢁ3452.073
185.641
1.646
ꢁ980.199
186.799
1.661
ꢁ1085.382
191.465
1.459
Zero-point vibrational energy (kcal molꢁ1
Rotational constants (GHz)
)
0.067
0.057
0.049
0.048
0.037
0.056
0.044
0.065
0.056
0.048
0.047
0.036
0.054
0.043
Total entropy (cal molꢁ1 Kꢁ1
Translational entropy (cal molꢁ1 Kꢁ1
Rotational entropy (cal molꢁ1 Kꢁ1
Vibrational entropy (cal molꢁ1 Kꢁ1
)
141.791
42.831
35.040
63.920
141.342
42.974
35.356
63.011
138.956
43.130
35.706
60.120
145.706
43.167
35.692
66.846
148.815
43.553
36.215
69.047
142.288
43.014
35.399
62.875
149.564
43.269
35.981
70.314
)
)
)
The total entropy of 8 is found to be higher than those of 2–7. It
is evident that among all azines that the azine with electron-with-
drawing substituent in the phenyl ring with lower energy gap
between HOMO and LUMO orbitals (azine 8) is found to have
higher entropy.
Acknowledgment
The authors thank the NMR Research Centre, Indian Institute of
Technology, Chennai for recording the NMR spectra.
Appendix A. Supplementary material
MEP surfaces
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.03.093.
Three dimensional distribution of molecular electrostatic
potential (MEP) is highly useful in predicting the reactive behaviour
of the molecule. The MEP surface is on overlaying of the eletrostatic
potential on to the isoelectron density surface. This is a valuable
tool for describing over all molecule charge distribution as well as
anticipating sites of electrophilic addition. In all azines region of
negative charges (red colour) is seen around the electronegative
nitrogens N(1) and N(2). Region of negative charge (red colour) is
also seen around the electro negative oxygen O(38) in azine 4 and
O(39) and O(40) in azine 8. The red region is susceptible for
electrophillic attack. Blue colour represents strongly positive region
and the predominant green region in the MEP surfaces corresponds
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prepared and characterized by FT-IR, 1H, 13C NMR, Mass and UV
spectral studies. The Gaussian-03 B3LYP/6-311+G(d,p) calculations
on these azines are used to evaluate the heat of formation of the
different conformers, to identify the stable conformation, to deter-
mine the dipole moment, polarizability, first hyperpolarizability,
bond lengths, bond angles and torsional angles, MEP surface,
HOMO and LUMO energies. All the azines are found to be polar
molecules having non-zero dipole moment components. These
result in large microscopic first hyperpolarizabilities and hence
have a good microscopic NLO behaviour. Among the azines 2–8,
azine 8 is found to have a good NLO behaviour that is indicated
by its high first hyperpolarizability value. The NLO behavioural
analysis of azine 8 has been studied experimentally by SHG test.
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pared to other azines. The thermodynamic properties for all the
azines are also calculated. The total entropy for 8 is found to be
higher than those of 2–7.
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