Physicochemical studies of molecular hyperpolarizability of imidazole derivatives

Article abstract of DOI:10.1016/j.saa.2011.02.024

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, arylaldehyde, arylamine and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, g

Full text of DOI:10.1016/j.saa.2011.02.024

Spectrochimica Acta Part A 79 (2011) 137–147
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Physicochemical studies of molecular hyperpolarizability of imidazole
derivatives
Jayaraman Jayabharathi∗, Venugopal Thanikachalam, Natesan Srinivasan,
Marimuthu Venkatesh Perumal, Karunamoorthy Jayamoorthy
Department of Chemistry, Annamalai University, Annamalainagar, 608 002 Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of substituted imidazoles have been synthesized in very good yield under solvent free condition
by grinding 1,2-diketone, arylaldehyde, arylamine and ammonium acetate in the presence of molecular
iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practi-
cally and economically attractive and the imidazoles are characterized by NMR spectra, X-ray, mass and
CHN analysis. The push–pull character of series of imidazoles have been analyzed by the quotient of the
occupations of the bonding (␲) and anti-bonding (␲*) orbitals of the central linking –N C–C C– unit.
Excellent correlation of the push–pull parameter with the corresponding bond lengths dC and dC
Received 22 November 2010
Received in revised form 12 February 2011
Accepted 15 February 2011
Keywords:
NMR
DFT
N
C
strongly recommend both the occupation quotients (ꢀ*/ꢀ) and the corresponding bond lengths are rea-
sonable sensors for quantifying the push–pull character and for the molecular hyperpolarizability ß0 of
these compounds. To support the experimental results, theoretical calculations (heat of formation, NLO,
NBO and vibrational analysis) were also made. Within this context, reasonable conclusions concerning
the steric hindrance in the chromospheres, push–pull character, hyperpolarizability of the imidazoles
and their application as NLO materials will be drawn.
NLO
NBO
Occupation coefficients
Vibrational analysis
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
dazoles using iodine as the catalyst. Searching for organic materials
with nonlinear optical (NLO) properties is usually concentrated
Designing of “green” experimental protocol is an enormous
challenge to chemists to improve the quality of the environment for
present and future generations. Compounds with an imidazole ring
system have many pharmacological properties [1,2]. Though there
are several methods reported [3,4] in the literature for the synthe-
sis of imidazoles, they suffer from one or more disadvantages such
as harsh reaction conditions, poor yields, prolonged time period,
use of hazardous and often expensive acid catalysts. Since organic
solvents are high on the list of damaging chemicals, in recent
years solid-state organic reactions have caused great interest.
Recently, molecular iodine received considerable attention as an
inexpensive, nontoxic, readily available catalyst for various organic
transformations, affording the corresponding products in excellent
yields with high selectivity. Owing to numerous advantages asso-
ciated with this eco-friendly element, iodine has been explored as
a powerful catalyst for various organic transformations [5]. During
the course of our studies towards the development of new route to
the synthesis of biologically active heterocycles, we wish to report a
simple and an efficient method for the synthesis of substituted imi-
on molecules with donor–acceptor ␲-conjugation (D–␲–A) and
deals with the systematic investigation of substituent effects on
the degree of ␲-conjugation, steric hindrance and the hyperpolar-
izability of the substances. Besides, geometrical arrangement of the
molecules in the solid state, their interaction and other physic-
ochemical properties (e.g. strong intramolecular charge-transfer
absorptions) and engineering possibilities are also important [6].
At present, there is an insufficient understanding of all influences
for designing optimal NLO materials, even if the influencing factors
in certain classes of D–␲–A compounds were theoretically stud-
ied [7]. To quantify the push–pull effect in D–␲–A compounds,
bond length alternation (BLA) and out-of-plane distortions of the
polarized C C double bonds, available from X-ray studies, have
been employed for a long time [8]. Alternatively, dipole moment
measurements [9], bond lengths [10], barriers to rotation about
the partial C C double bonds [11] (from dynamic NMR studies),
and the occupation quotients (ꢀ/ꢀ*) [12] of the bonding (to quan-
tify the acceptor activity) and anti-bonding orbital (to quantify the
donor activities) of these C C double bonds were adopted. Not
only the push–pull effect in D–␲–A compounds could be quantified,
but also a linear dependence of the push–pull quotient (ꢀ*/ꢀ) on
molar hyperpolarizability of these compounds were detected [13].
Thus, ꢀ*/ꢀ proves to be an easily accessible, general and sensitive
∗
Corresponding author. Tel.: +91 9443940735.
E-mail address: jtchalam2005@yahoo.co.in (J. Jayabharathi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.02.024

138
J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
parameter of the donor–acceptor quality of compounds for poten-
tial NLO applications. Furthermore, we have reported the Quantum
chemical analysis [14] ((DFT/B3LYP) method with 6-311G++ (d,p)
as basis set) of imidazole derivatives 1–6 (heat of formation, geo-
metrical structure, vibration wave numbers, NLO and NBO analysis)
and the optimized geometrical parameters obtained by DFT cal-
culation is in good agreement with single crystal XRD data. The
Mulliken and NBO charge analysis were also calculated and dis-
cussed about the more basic nature of the nitrogen atom of the
imidazole derivatives. The electric dipole moment (ꢁ) and the first-
hyperpolarizability (ˇ) value of the investigated molecules have
been studied by both experimentally and theoretically which reveal
that they have non-linear optical (NLO) behavior with non-zero val-
ues. These chromophores possess a more appropriate ratio of off
2.3.2. Natural Bond Orbital (NBO) analysis
The second order Fock matrix was carried out to evaluate the
donor–acceptor interactions in the NBO analysis [17]. For each
donor (i) and acceptor (j), the stabilization energy E(2) associated
with the delocalization i → j is estimated as
F(i, j)2
E(2) = ꢂEij = q
(4)
i εj − εi
where qi is the donor orbital occupancy, εi and εj are diagonal ele-
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
electron donors and electron acceptors.
2.3.3. General procedure for the synthesis of 2-aryl imidazole
derivatives (1–6)
– diagonal versus diagonal ˇ tensorial component (r = ˇxyy/ˇxxx
)
which reflects the inplane nonlinearity anisotropy since they have
largest ꢁˇ0 values, the reported imidazoles can be used as potential
NLO materials.
A mixture of substituted aldehyde (1 mmol), benzil (1 mmol),
ammonium acetate (2.5 mmol) and iodine (15 mol %) were grained
in a mortar at room temperature for appropriate time. The reac-
tion was monitored by TLC and the reaction mixture was treated
with aqueous Na2S2O3, the formed crude was purified by column
chromatography (n-hexane:ethyl acetate (9:1) (Scheme 1).
2. Experimental
2.1. Optical measurements and composition analysis
2.3.4. 2-(4-Fluorophenyl)-4,5-dimethyl-1-p-tolyl-1H-imidazole
NMR spectra were recorded for the imidazole derivatives (1–6)
on a Bruker 400 MHz. The ultraviolet-visible (UV–Vis) spectra were
measured on a UV–Vis spectrophotometer (Perkin Elmer, Lambda
35) and corrected for background due to solvent absorption. Mass
spectra were recorded on a Varian Saturn 2200 GCMS spectrometer.
(1)
Yield: 50%. mp 130 ◦C, Anal. calcd. for C18H17FN2: C, 77.12;
H, 6.11; N, 9.99. Found: C, 77.00; H, 5.98; N, 9.03. FTIR (cm−1
)
1519,1598, 1647, 2364, 2855, 2916, 3540, 3751. 1H NMR (400 MHz,
CDCl3): ı 2.01 (s, 3H), 2.29 (s, 3H), 2.43 (s, 3H), 6.87–7.34 (aromatic
protons). 13C (100 MHz, CDCl3): ı 9.53, 12.69, 21.18, 114.92, 115.10,
125.44, 127.16, 129.89, 130.20, 133.35, 135.13, 138.57, 144.28,
161.26, 163.23. MS: m/z 280.00, calcd. 280.14.
2.2. Non-linear optical measurements
The second harmonic generation efficiency was assessed by
Kurtz powder technique [15] at IISc., Bangalore, India. It is a well
established tool to evaluate the conversion efficiency of nonlin-
ear optical materials. A Q-switched Nd:YAG laser operating at the
fundamental wavelength of 1064 nm, generating about 4.1 mJ and
pulse width of 8 ns was used for the present experimental study.
The input laser beam was passed through an IR reflector and then
incident on the powder form of the specimen, which was packed
in a glass capillary tube. The output energy was detected by a pho-
todiode detector integrated with oscilloscope assembly.
2.3.5. 2-(4-Fluorophenyl)-1,4,5-triphenyl-1H-imidazole (2)
Yield: 60%. mp 242 ◦C, Anal. calcd. for C27H19FN2: C, 83.05; H,
4.90; N, 7.17. Found: C, 82.00; H, 5.00; N, 4.78. FTIR (cm−1) 1256,
1645, 2434, 2990, 3456. 1H NMR (400 MHz, CDCl3): ı 6.92 (d, 2H),
7.49–7.80 (m, 15H), 7.90 (d, 2H) (aromatic protons). 13C (100 MHz,
CDCl3): ı 126.55, 127.38, 128.10, 128.38, 128.93, 130.69, 131.12,
134. 46, 137.14, 138.29, 146.91. MS: m/z 390.00, calcd. 390.45.
2.3.6. 2-(4,5-Diphenyl-1H-imidazol-2-yl)phenol (3)
Yield: 62%. mp 210 ◦C, Anal. calcd. for C21H16N2O: C, 80.75;
2.3. Computational details
H, 5.16; N, 8.97. Found: C, 79.12; H, 5.20; N, 7.64. FTIR (cm−1
)
1640, 2462, 3008, 3462, 3658. 1H NMR (400 MHz, CDCl3): ı,
6.93–6.99 (m, 7H), 7.26–7.52 (m, 7H), 8.04 (s, 1H),12.97 (brs,
1H) (aromatic protons), 13C (100 MHz, CDCl3): ı 113.36,117.29,
119.32, 125.42,129.09, 130.54, 146.33, 157.17 MS: m/z 312.00,
calcd. 312.36.
Quantum mechanical calculations were carried out using
Gaussian-03 program [14]. As the first step of our DFT calculation,
the geometry taken from the starting structure was optimized.
2.3.1. Hyperpolarizability calculation
The density functional theory has been used to calculate the
dipole moment (ꢁ), mean polarizability (˛) and the total first static
hyperpolarizability (ˇ) [16] for 1–6 in terms of x, y, z components
and are given by following equations.
2.3.7. 2-(4,5-Diphenyl-1-p-tolyl-1H-imidazol-2-yl)phenol(4)
Yield: 65%. mp 215 ◦C, Anal. calcd. for C28H22N2O: C, 83.56; H,
5.51; N, 6.96. Found: C, 83.00; H, 5.20; N, 6.02. FTIR (cm−1) 1638,
2465, 2996, 3456, 3598. 1H NMR (400 MHz, CDCl3): ı 2.27 (s, 3H),
6.80 (d, 2H), 7.84 (d, 2H), 7.16–7.25 (m,7H), 7.45–7.51 (m, 6H), 9.31
(s, 1H),12.50 (brs, 1H) (aromatic protons), 13C (100 MHz, CDCl3): ı
9.53, 114.73, 120.80, 126.06, 126.33, 127.15, 127.40, 145.87, 157.08.
MS: m/z 402.00, calcd. 402.17.
ꢁ = (ꢁ2x + ꢁ2y + ꢁz2)1/2
(1)
(2)
1
3
˛ = (˛xx + ˛yy + ˛zz
)
ˇtot = (ˇx2 + ˇy2 + ˇz2)1/2 (or) ˇtot = [(ˇxxx + ˇxyy + ˇxzz
)
2
2.3.8.
2 + (ˇzzz + ˇzxx + ˇzyy)2]1/2
(3)
2-(2-Methoxyphenyl)-4,5-diphenyl-1-p-tolyl-1H-imidazole (5)
+ (ˇyyy + ˇyzz + ˇyxx
)
Yield: 62%. mp 235 ◦C, Anal. calcd. for C29H24N2O: C, 83.63;
H, 5.81; N, 6.73. Found: C, 82.98; H, 5.01; N6.01. FTIR (cm−1
)
1230, 1450, 1605, 2924, 3512, 3614. 1H NMR (400 MHz, CDCl3):
ı 2.20 (s, 3H), 3.80 (s, 3H),2.40 (s, 3H), 6.77 (d, 2H), 7.05–7.50 (m,
14H), 8.03 (s, 2H) (aromatic protons). 13C (100 MHz, CDCl3): ı 9.53,
The ˇ components of Gaussian output are reported in atomic
units and therefore the calculated values are converted into e.s.u.
units (1 a.u.= 8.3693 × 10−33 e.s.u.).

J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
139
Table 1
Selected bond lengths (Å), bond angles (◦) and torsional angles (◦) of 1.
Bond lengths (Å)
Experimental
XRD (Å)
Bond angles (◦)
Experimental
XRD (◦)
Torsional angles (◦)
Experimental
XRD (◦)
N1–C2
N1–C5
N1–C11
N3–C2
N3–C4
1.38(1.42)
1.84(1.41)
1.44(1.41)
1.32(1.36)
1.37(1.40)
1.46(1.46)
1.36(1.42)
1.50(1.47)
1.49(1.47)
1.38(1.41)
1.38(1.41)
1.39(1.39)
1.39(1.40)
1.38(1.40)
1.39(1.41)
1.39(1.40)
1.40(1.40)
1.39(1.39)
1.32(1.41)
1.38(1.39)
1.36(1.35)
C2–N1–C5
106.9(106.7)
128.6(127.7)
123.3(125.4)
106.5(106.4)
110.5(110.8)
126.4(124.6)
123.0(124.6)
110.2(110.0)
121.4(123.7)
128.4(126.3)
105.9(106.1)
122.5(128.7)
131.6(128.7)
119.8(120.3)
119.2(120.8)
121.0(119.0)
119.1(120.1)
121.2(120.9)
118.3(119.0)
121.5(122.0)
119.0(118.9)
124.2(120.9)
117.7(119.2)
118.0(119.9)
121.2(120.4)
118.7(119.5)
122.1(122.2)
118.7(119.6)
121.3(120.4)
C5–N1–C2–N3
−0.05(0.22)
176.9(179.0)
167.4(174. 9)
−15.60(−0.04)
0.51(0.212)
178.2(179.9)
−167.8(175.0)
10.9(5.03)
C2–N1–C11
C5–N1–C11
C2–N3–C4
C5–N1–C2–C21
C11–N1–C2–N3
C11–N1–C2–C21
C2–N1–C5–C4
C2–N1–C5–C51
C11–N1–C5–C4
C11–N1–C5–C51
C2–N1–C11–C12
C2–N1–C11–C16
C5–N1–C11–C12
C5–N1–C11–C16
C4–N3–C2–N1
N1–C2–N3
C2–C21
C4–C5
N1–C2–C21
N3–C2–C21
N3–C4–C5
N3–C4–C41
C5–C4–C41
N1–C5–C4
C4–C41
C5–C51
C11–C12
C11–C16
C12–C13
C13–C14
C14–C15
C15–C16
C21–C22
C21–C26
C22–C23
C23–C24
C25–C26
F4–C24
117.6(133.4)
−64.96(47. 9)
−76.77(52.9)
100.7(126.2)
−0.43(0.138)
177.6(178.2)
−0.77(0.00)
178.0(179.2)
−18.3(43.67)
164.9(138.8)
158.3(134.1)
−18.4(43.36)
−0.79(0.136)
−179.3(179.3)
−177.9(−179.0)
−0.57(1.560)
−177.0(179.4)
−0.3(0.210)
177.5(179.6)
−0.1(0.530)
0.5(0.075)
N1–C5–C51
C4–C5–C51
N1–C11–C12
N1–C11–C16
C12–C11–C16
C11–C12–C13
C12–C13–C14
C13–C14–C15
C14–C15–C16
C11–C16–C15
C2–C21–C22
C2–C21–C26
C22–C21–C26
C21–C22–C23
C22–C23–C24
C23–C24–C25
C24–C25–C26
C21–C26–C25
C4–N3–C2–C21
C2–N3–C4–C5
C2–N3–C4–C41
N1–C2–C21–C22
N1–C2–C21–C26
N3–C2–C21–C22
N3–C2–C21–C26
N3–C4–C5–N1
N3–C4–C5–C51
C41–C4–C5–N1
C41–C4–C5–C51
N1–C11–C12–C13
C16–C11–C12–C13
N1–C11–C16–C15
C12–C11–C16–C15
C11–C12–C13–C14
C13–C14–C15–C16
C17–C14–C15–C16
C14–C15–C16–C11
C2–C21–C22–C23
C2–C21–C26–C25
F4–C22–C23–C24
F4–C24–C25–C26
−0.02(0.017)
178.5(179.4)
0.4(0.351)
−177.2(178.3)
−177.3(−178.3)
179.8(179.5)
179.7(179.9)
Values in the parenthesis are corresponding to the theoretical values.
55.1 115.25, 125.05, 126.47, 127.50, 127.69, 128.68, 129.69 130.45,
145.61. MS: m/z 416.00, calcd. 416.19.
2.3.9. 4-(4,5-Diphenyl-1-p-tolyl-1H-imidazol-2-yl)phenol (6)
Yield: 58%. Mp 231 ◦C, Anal. Calcd. For C28H22N2O: C, 83.56; H,
5.51; N, 6.96. Found: C, 82.58; H, 5.23; N 6.56. FTIR (cm−1) 1245,
1542, 1635, 2876, 3589, 3721. 1H NMR (400 MHz, CDCl3): ı 2.20 (s,
3H), 6.93 (d, 2H), 7.53–7.89 (m, 14H), 7.92 (d, 2H), 12.52 (brs, 1H)
(aromatic protons). 13C (100 MHz, CDCl3): ı 9.52, 113.20, 119.76,
125.01, 127.50, 127.69, 130.45, 144.78, 158.30 MS: m/z 402.00,
calcd. 402.70.
3. Results and discussion
3.1. Steric hindrance in imidazoles: X-ray analysis
X-ray data of (1) (Table 1) reveal that the imidazole ring is essen-
tially planar [18] and makes dihedral angles of 72.33◦ and 18.71◦
with the methylphenyl and fluorophenyl rings, respectively. The
dihedral angle between the two benzene rings is 75.05◦ (Fig. 1).
The crystal packing is stabilized by intermolecular C–H(N hydro-
gen bonds. The crystal packing is stabilized by C12–H12(N3 (2 − x,
1 − y, −z) and C16–H16(N3 (2 − x, 2 − y, −z) intermolecular hydro-
gen bonds (Table 2, Fig. 2). In order to eliminate crystal packing
effect in the solid state, the molecular geometry of 1–6 is further
examined by DFT calculation [15] to make necessary comparison.
Three key twists, designated as ˛, ˇ and ꢃ have been examined. ˛
is used to indicate the twist of imidazole ring from the aromatic
six-membered ring at C(2), ˇ and ꢃ are used for twists of imidazole
Fig. 1. Ortep diagram of (1).

140
J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
lated with fluorescent property, the larger the ˛ twist, the more
drop the fluorescence quantum yield. Such a clear correlation indi-
cates the importance of coplanarity between imidazole and the
aromatic ring at C(2). This correlation can be ascribed to the con-
jugation rigidity. When the two adjacent aromatic species are in
a coplanar geometry, the p-orbitals from the C–C bond connect-
ing the two species will have maximal overlapping and the two
rings will have a rigid and delocalized conjugation, as the result,
the bond is no longer a pure single bond, as evident from the X-
ray data of (1). The present bond distance of C2–C21 is 1.464(4) Å
(Table 1) is shorter than the regular single bond distance between
two sp2 carbons (1.48 A) [18], because of delocalization. When the
˚
two rings are deviated from each other, the p-orbital overlapping
will be reduced. All these XRD data are in good agreement with the
theoretical values. However, from the theoretical values it can be
found that most of the optimized bond lengths, bond angles and
dihedral angles are slightly higher than that of XRD values. These
deviations can be attributed to the fact that the theoretical calcu-
lations were aimed at the isolated molecule in the gaseous phase
whereas the XRD results were aimed at the molecule in the solid
state.
3.2. Second harmonic generation (SHG) studies of 1–6
Second harmonic signal of 50 mV, 48 mV, 85 mV, 70 mV, 69 mV
and 40 mV was obtained for 1–6 by an input energy of 4.1 mJ/pulse.
But the standard KDP crystal gave a SHG signal of 110 mV/pulse
for the same input energy. The second order nonlinear efficiency
will vary with the particle size of the powder sample [19]. Higher
efficiencies are achieved by optimizing the phase matching [20].
On a molecular scale, the extent of charge transfer (CT) across the
NLO chromospheres determine the level of SHG output, the greater
the CT and the larger the SHG output.
Fig. 2. The packing of fpdmti (1) viewed down the a axis. Dashed lines indicate
hydrogen bonds. H atoms not involved in hydrogen bonding have been omitted.
3.3. Comparison of ꢁˇ0
The overall polarity of the synthesized imidazole derivatives
is small when their dipole moments aligned in a parallel fashion
(Fig. 4). When the electric field is removed, the parallel alignment
of the molecular dipole moments begins to deteriorate and even-
tually the imidazole derivatives loses its NLO activity. The ultimate
goal in the design of polar materials is to prepare compounds which
have their molecular dipole moments aligned in the same direction
[21].
Theoretical investigation can play an important role in under-
standing structure–property relationship, which is able to assist
in designing novel NLO chormophores. The electrostatic first
hyperpolarizability (ˇ) and dipole moment (ꢁ) of the imidazole
chromophores have been calculated by using Gaussian 03 package
[14]. From Table 4, it is found that all the imidazole chromophores
show larger ꢁgˇ0 values, which is attributed to the positive con-
tribution of their conjugation. The chromophore 3 exhibits larger
nonlinearity than other chromophores and its ꢄmax is red-shifted.
Therefore, it is clear that the hyperpolarizability is a strong func-
tion of the absorption maximum. Since even a small absorption
at the operating wavelength of optic devices can be detrimental,
it is important to make NLO chromophores as transparent as pos-
sible without compromising the molecule’s nonlinearity. Thermal
stability of the imidazole chromophores was estimated by thermo
gravimetric analysis (TGA). All samples show appreciable decom-
position temperature (Td) and their iridium complexes are ideal
candidates for device application [21–23].
Table 2
Hydrogen-bond geometry (Å) of 1.
D–H· · ·A
D–H
H· · ·A
D(A
D–H· · ·A
C12–H12· · ·N3
C16–16· · ·N3
0.93
0.93
2.55
2.60
3.3714
3.5154
148
167
ring from phenyls at C(5) and C(4) positions, respectively (Fig. 3). By
comparisonof results inTable3severaladditional interestingstruc-
tural features can be concluded that the ꢃ twist is always smaller
than the ˇ twist. The ˇ twist originates from the interaction of sub-
stituent at N(1) of the imidazole with the methyl group at C(5)
whereas the ꢃ twist is a result of the interaction of the methyl group
at C(4) with the other one at C(5). The ˇ twist always increases
upon the substitution at N(1) of the imidazole derivatives com-
pared to the parent counterparts and the substitution increases the
ˇ twist but decreases the ꢃ twist. The present structural informa-
tion allows us to further explore the correlation between structural
features and fluorescent property. It reveals that ˛ twist is corre-
Table 3
Deviation parameters (◦) of imidazole from other rings.
Compound
(˛)
-43.68
42.16
−21.90
−89.62
−139.70
42.16
(ˇ)
5.03
(ꢃ)
1
2
3
4
5
6
−179.02
−178.87
−179.22
−179.03
−178.87
−178.87
−2.12
To determine the transference region and hence to know the
suitability of these compounds (1–6) for microscopic nonlinear
optical applications, the UV–visible spectra have been recorded
by using the spectrometer in the range of 190–1100 nm. These
1.49
−5.08
−2.12
−2.12

J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
141
Fig. 3. Schematic presentation of ˛, ˇ, and ꢃ.
compounds show absorption spectra in the UV region between
238 and 303 nm. The increased transparency in the visible region
might enable the microscopic NLO behavior with non-zero values
[24–26]. All the absorption bands are due to ␲ → ␲* transi-
tions. The ˇ values (Table 5) computed here might be correlated
with UV–visible spectroscopic data in order to understand the
molecular-structure and NLO relationship in view of a future opti-
mization of the microscopic NLO properties. The band at around
303.9 nm exhibits a solvatochromic shift, characteristic of a large
dipole moment and frequently suggestive of a large hyperpo-
larizability. These compounds show red shift in absorption with
increasing solvent polarity, accompanied with the upward shifts
non-zero values in the ˇ-components.
3.4. Octupolar and dipolar components of three types of
chromophores
These chromophores possess a more appropriate ratio of off-
diagonal versus diagonal ˇ tensorial component (r = ˇˇxyy/ˇxxx
)
which reflects the inplane nonlinearity anisotropy and the largest
Table 4
Characterization of chromophores 1–6.
Chromophore
ꢄmax (nm)
(
g
(D)
ˇ0/10−30
(gˇ0/10−48
Td (◦C)
r
ꢅ
(esu)
(esu)
1
2
3
4
5
6
290.5
291.5
303.9
248.0
238.0
245.0
2.848
2.092
4.838
3.513
2.886
2.022
62.759
40.353
85.292
68.028
65.248
23.039
078.7
68.2
412.6
239.0
188.3
46.6
336
348
275
360
312
282
−0.03
−0.05
−0.002
0.03
0.04
0.03
0.42
0.43
0.34
0.26
0.24
0.25

142
J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
Table 5
Electric dipole moment (D), polarizability (˛) and Hyperpolarizability (ˇtotal) of 1–6 calculated using B3LYP/6-31G(d,p).
Parameter
1
2
3
4
5
6
Dipole moment (D)
ꢁx
ꢁy
ꢁz
ꢁtotal
0.989
2.985
0.644
−0.2193
1.667
2.256
1.580
1.002
4.838
0.6248
2.829
1.308
3.513
0.586
−1.278
3.578
0.489
2.249
−1.126
−0.716
2.848
2.092
2.886
2.022
Polarizability (˛)
˛
˛
˛
˛
˛
˛
264.263
13.329
112.687
0.799
4.861
262.696
28.634
356.011
332.008
−2.059
113.913
7.612
44.206
261.482
34.945
397.513
−5.407
205.714
404.677
−6.956
218.053
−18.396
−2.989
380.292
49.549
407.74
−4.441
202.304
xx
−17.764
181.969
0.706
20.134
355.967
44.161
xy
yy
−20.559
−17.275
xz
2.476
8.552
yz
364.633
47.812
360.502
47.945
zz
˛ × 10−24 (esu)
Hyperpolarizability
ˇxxx
ˇxxy
ˇxyy
ˇyyy
ˇxxz
ˇxyz
ˇyyz
ˇxzz
736.149
−234.895
−71.618
12.649
−79.295
−23.718
20.984
−14.618
−93.660
1.662
1467.095
17.143
−3.778
−1.530
28.022
1274.941
10.089
36.845
1235.909
−14.388
47.367
674.220
11.716
22.592
−43.675
−19.818
3.327
32.446
11.864
7.766
91.762
168.783
−30.499
−56.724
−537.059
29.728
188.955
−17.898
−57.310
−537.119
49.598
128.571
−0.123
−31.647
−556.211
9.054
−3.221
−37.747
2.624
61.696
−2.350
−481.147
23.894
ˇyzz
49.597
ˇzzz
−285.077
−24.900
−117.661
−232.961
−238.553
−143.166
ˇ × 10−31 (esu)
62.759
40.353
85.292
68.028
65.247
23.039
esu: electrostatic unit; (1 a.u. = 8.3693 × 10−33 e.s.u.); x, y, z: principle axis.
ꢁˇ0 values. The difference of the ˇxyy/ˇxxx ratios for these chro-
mophores can be well understood by analyzing their relative
molecular orbital properties. The electrostatic first hyperpolariz-
abilities (ˇ0) and dipole moment (ꢁ) of the chromophores have
been investigated theoretically and it is found that the ground
state dipole moments of the six chromophores are in the order
ꢁ(3) > ꢁ(4) > ꢁ(5) > ꢁ(1) > ꢁ(6) > ((2) and this can be well under-
stood by the vector additive model. The sequence of their ˇ0 values
are in the order of ˇ0(3) > ˇ0(4) > ˇ0(5) > ˇ0(1) > ˇ0(6) > ˇ0(2). This
observed sequence can be explained by the reduced planarity in
such chromophores caused by the steric interaction between the
two phenyl rings at C(2) and N(4) atoms. Hence, the steric interac-
tion must be reduced in order to obtain larger ˇ0 values.
The ˇ tensor [25] can be decomposed in a sum of dipolar
2D
(
J=1ˇ) and octupolar (2J=D3ˇ) tensorial components, and the ratio
of these two components strongly depends on their ‘r’ ratios. The
zone for r > r2 and r < r1 corresponds to a molecule of octupo-
lar and dipolar respectively. The critical values for r1 and r2 are
√
√
√
√
√ √
(1 − 3)/ 3( 3+1) = −0.16 and ( 3 + 1)/ 3( 3 − 1) = 2.15, respec-
tively. Complying with the Pythagorean theory and the projection
closure condition, the octupolar and dipolar components of the ˇ
tensor can be described as:
3
4
2D
||j=1ˇ|| = [(ˇxxx + ˇxyy
)
2 + [(ˇyyy + ˇyxx)2]
(5)
(6)
1
2 + [(ˇyyy + ˇyxx)2]
2D
||j=3ˇ|| = [(ˇxxx + 3ˇxyy
)
4
2D
2D
The parameter
ꢅ
2D[ꢅ2D = (||j=3ˇ||)/(||j=1ˇ||)] is convenient to
compare the relative magnitudes of the octupolar and dipolar com-
ponents of ˇ. The observed positive small ꢅ values (Table 4) of
imidazole derivatives reveal that the ˇiii component cannot be zero
and these are dipolar component. Since most of the practical appli-
cations for second order NLO chromophores are based on their
dipolar components, this strategy is more appropriate for designing
highly efficient NLO chromophores.
3.5. Bond length and occupation coefficient for quantifying the
push–pull effect in imidazoles
The two push–pull parameters [bond lengths d (Å) and occupa-
tion quotients ꢀ*/ꢀ] of the partial C N and C C bonds of the linking
chain N C–C C were calculated (Table 6) and the corresponding
values are correlated in Fig. 5. The linear correlation indicate that
with increasing donor–acceptor character of the imidazoles 1–6
the two partial C N and C C bonds are elongated, thereby the
occupation quotients ꢀ*/ꢀ increased. Thus the imidazoles can be
confirmed to be strongly polarized, ␲-delocalized materials which
should exhibit NLO behavior.
Fig. 4. Orientation of dipole moments.

J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
143
Table 6
Occupation numbers of antibonding ␲* and bonding ␲ orbitals of the corresponding partial C N and C C double bonds, molecular hyperpolarizability (ˇ0) and dipole
moments (ꢁ) of 1–6.
Compound
ꢀ
ꢀ*
ꢀ*/ꢀ
d (Å)
ꢀ*/ꢀ/2
0.189
0.151
0.233
0.207
0.191
0.008
1
2
3
4
5
6
1.670
1.653
1.641
1.654
1.681
1.971
0.363
0.364
0.395
0.369
0.350
0.019
0.217
0.220
0.241
0.223
0.208
0.010
1.356
1.254
1.263
1.324
1.362
1.215
3.6. Natural Bond Orbital (NBO) analysis
NBO analyses have been performed for 1–6 at the DFT/B3LYP/6-
31++G(d,p) level in order to elucidate the intramolecular,
hybridization and delocalization of electron density within the
molecule. The intramolecular interactions are formed by the orbital
overlap between (C–C) and ␴*(C–C) bond orbital which results
intramolecular charge transfer (ICT) causing stabilization of the sys-
tem. These interactions are observed as increase in electron density
(ED) in C–C antibonding orbital that weakens the respective bonds
[27].
The importances of hyperconjugative interaction and electron
density transfer (EDT) from lone pair electrons to the anti-
bonding orbital have been analyzed and the results [28] are
presented in Tables 7 and 8. Several donor–acceptor interactions
are observed in 1 and among the strongly occupied NBOs, the
most important delocalization sites are in the ␲ system and in
the lone pairs (n) of the oxygen, fluorine and nitrogen atoms of
1. The ␴ system shows some contribution to the delocalization,
and the important contributions to the delocalization corre-
sponds to the donor–acceptor interactions are C6–C10 → C15–C19,
C16–C19 → C6–C10, C17–H20 → C15–C16, C18–H22 → C17–H20,
C18–H22 → C17–H20, C27–C28 → C29–C32, C29–C32 → C30–C34,
C30–C34 → C27–C28, C40–C43 → C41–C45, C41–C45 → C38–C39,
C29–C32 → C30–C34 and C29–C32 → C30–C34
Fig. 5. Correlation of bond length (Å) and occupation co-efficient.
These two parameters [bond lengths dN (Å) and occupation
C
quotients ꢀ*/ꢀ] quantifying the donor–accepter properties of the
studied imidazoles, the molecular hyperpolarizability have been
correlated with the mean of the sum of ꢀ*/ꢀ N C and the ꢀ*/ꢀ C
quotients. A clear linear dependence (Fig. 6) of the two parameters
shows that, the polarity of these compounds for potential appli-
cation as NLO material is important, but not deciding. Molecules
of higher hyperpolarizability have larger dipole moments used as
potential NLO molecules (characterized by bond lengths, occupa-
tion p*/p quotients and dipole moment variations) [25].
C
The charge distribution of 1 was calculated by the NBO and
Mulliken methods (Fig. 7). These two methods predict the same
tendencies i.e., among the nitrogen atom N4 and N5, N5 is consid-
ered as more basic site [29]. The charge distribution shows that
the more negative charge is concentrated on N5 atom whereas the
partial positive charge resides at hydrogens.
3.7. Vibrational assignments
The molecule (1) has 38 atoms and hence can have 108 normal
modes of vibrations. According to the molecule possess a non-
planar structure with C1 point group symmetry. The observed FT-IR
and various modes of frequencies are calculated theoretically. Only
few selected vibrations are discussed and displayed in Table 9
(Fig. 8a and b).
3.7.1. O–H vibrations
In the case of alcohols a very sharp band appears around
3600 cm−1 in very dilute solution using non-polar solvents if
intramolecular hydrogen bonding is absent [30]. In bonded form, a
broad and intense band appears in the region 3200–3550 cm−1. In
the present work the broad band centered at 3427 cm−1 is assigned
to O–H stretching modes for 4 and 6. The calculated theoretical OH
vibrations after scaling are in good agreement with experimental
vibrations.
3.7.2. C–H vibrations
Presence of band in the region 2700–3000 cm−1 is the charac-
teristic region for the identification of C–H stretching vibrations
Fig. 6. Correlation of molecular hyper polarizability and mean of the sum of occu-
pation co-efficient.

144
J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
Table 7
Significant donor–acceptor interactions of (1) and their second-order perturbation energies (kcal/mol).
Donor (I)
Type
ED/e
Acceptor (J)
Type
ED/e
E(2) a.u
E(j)–E(i)
F(I, j)
C1–C2(2)
C3–N5(2)
C6–C8(2)
C6–C8(2)
C6–C8(2)
C7–C9(2)
C7–C9(2)
C10–C11(2)
C10–C11(2)
C23–C25(2)
C23–C25(2)
C24–C26(2)
C24–C26(2)
C28–C30(2)
C28–C30(2)
LP(1)N4
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␲
␴
␴
␴
␲
1.81,620
1.83,922
1.64,093
1.64,093
1.64,093
1.69,281
1.69,281
1.65,543
1.65,543
1.67,726
1.67,726
1.68,388
1.68,388
1.65,174
1.65,174
1.57,526
1.93,041
1.96,627
1.91,538
C3–N5(2)
C1–C2(2)
C3–N5(2)
C7–C9
C10–C11
C6–C8(2)
C10–C11(2)
C6–C8(2)
C7–C9(2)
C24–C26(2)
C28–C30(2)
C23–C25(2)
C28–C30(2)
C23–C25(2)
C24–C26(2)
C1–C2(2)
C3–N5(2)
C23–C25(2)
C10–C11(2)
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
␲*
0.41,502
0.30,914
0.41,502
0.30,942
0.38,650
0.39,486
0.38,650
0.39,486
0.30,944
0.31,091
0.33,506
0.037,815
0.33,506
0.37,815
0.31,091
0.30,914
0.41,502
0.37,815
0.38,650
12.51
20.06
18.28
20.15
20.54
16.92
21.06
21.14
16.61
18.88
18.35
19.24
20.03
22.18
19.01
27.48
43.07
14.62
20.16
0.26
0.33
0.25
0.28
0.26
0.28
0.26
0.29
0.29
0.29
0.29
0.27
0.29
0.27
0.28
0.30
0.26
027
0.054
0.075
0.062
0.068
0.066
0.063
0.068
0.071
0.063
0.066
0.06
0.066
0.068
0.069
0.065
0.084
0.095
0.056
0.089
LP(1)N5
LP(1)N4
LP(3)F34
0.42
Table 8
Percentage of s and p-character on each natural atomic hybrid of the Natural Bond Orbital.
Bond (A–B)
C1–C2(2)
ED/Energy (a.u.)
EDA
%
EDB%
NBO
s%
0.00
p%
0.7149
0.6993
0.7131
0.7011
0.7006
0.7136
0.7075
0.7067
0.7221
0.6918
0.7027
0.7115
0.7148
0.6993
0.6463
0.7631
51.10
–
50.85
–
49.08
–
50.06
–
52.15
–
49.38
–
51.09
–
41.77
–
48.90
–
49.15
–
50.92
–
49.94
–
47.85
–
50.62
–
48.91
–
58.23
–
0.715(sp1.00
0.700(sp1.00
0.713(sp1.00
0.701(sp1.00
0.701(sp1.00
0.714(sp1.00
0.708(sp1.00
0.707(sp1.00
0.722(sp1.00
0.692(sp1.00
0.703(sp1.00
0.712(sp1.00
0.715(sp1.00
0.700(sp1.00
0.646(sp2.03
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
99.93
99.92
99.97
99.95
99.95
99.96
99.96
99.96
99.97
99.95
99.95
99.96
99.96
99.95
66.95
62.98
0.00
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
33.00
36.80
C6–C8(2)
C6–C8(2)
C7–C9(2)
C10–C11(2)
C23–C25(2)
C24–C26(2)
C28–C30(2)
0.763(sp1.71)
Fig. 7. Bar diagram of NBO charge versus Mulliken charges.

J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
145
Table 9
Vibrational assignments of 2-(4-fluorophenyl)-4,5-dimethyl-1-p-tolyl-1H-imidazole (1) at B3LYP/6-31G(d,p), HF/6-31G(d,p) and HF/6-311G(d,p) [harmonic frequency
(cm−1), IR, Raman intensities (Km/mol−1), reduced masses (amu), force constants (mdynÅ−1)].
SI. no
Calculated frequencies (cm−1
)
HF6-311G(d,p)
HF6-311G(d,p)
Vibrational assignment
B3LYP/6-31G(d,p)
HF/6-31G(d,p)
HF/6-311G(d,p)
Intensity
Activity
Reduced
mass
Force
constant
1
2
3
4
5
6
7
8
9
25
28
42
45
63
56
82
88
57
83
89
0.1
0.2
0.3
0.1
0.1
0.6
0.4
0.9
0.4
1.2
0.6
1.0
0.3
0.7
1.7
0.3
0.3
2.0
0.4
0.5
0.7
0.1
0.3
0.1
3.1
5.1
10.6
4.1
10.8
1.4
0.4
2.3
1.5
1.5
2.5
4.8
4.9
5.2
4.4
33.9
0.6
47.9
0.2
12.6
1.7
0.1
1.3
0.2
2.7
0.8
0.6
2.0
0.5
0.0
1.2
0.4
7.2
2.4
0.5
4.5
3.6
12.4
2.1
0.0
24.6
66.9
41.9
6.9
1.6
13.5
100.0
1.1
0.0
0.2
1.6
0.3
2.9
0.3
0.2
0.9
0.9
0.5
0.3
0.2
0.2
0.9
0.9
0.5
1.9
1.2
1.6
0.6
0.4
0.5
0.4
0.2
0.3
0.9
0.5
0.2
2.8
1.0
2.0
1.7
0.6
0.3
6.1
3.8
5.2
10.3
0.1
1.0
0.1
0.3
10.7
0.5
5.7
0.9
1.2
1.4
0.2
2.2
4.0
0.4
0.3
0.0
0.5
1.9
0.6
0.1
1.0
7.8
2.7
3.3
1.3
11.3
2.9
21.2
6.4
1.1
4.4
17.8
5.7603
4.3289
3.7603
3.8690
4.2220
4.1241
4.7156
4.7124
3.7642
2.1288
2.4846
2.2293
1.0717
3.2503
4.0932
1.9016
1.8405
2.7748
4.2833
4.8408
4.7321
3.9752
3.9030
3.1474
3.5720
3.1677
5.7285
5.4821
3.5932
6.4517
6.3223
5.0130
4.6861
4.0190
4.4320
4.4995
6.5058
5.5465
5.6627
1.3579
1.2332
1.5227
1.2253
4.5521
2.5711
2.3870
2.6680
2.6450
1.4767
1.4014
2.7551
2.0936
1.3510
1.3211
1.8670
1.3707
2.7189
1.6438
1.4839
2.0967
2.5829
1.2003
1.7622
1.2465
3.5100
3.6622
3.2355
4.7318
1.3832
1.5598
3.0529
0.0134
0.0216
0.0216
0.0331
0.0410
0.0526
0.0909
0.1209
0.1274
0.0775
0.1119
0.1064
0.0571
0.1913
0.2642
0.1393
0.1459
0.2555
0.4285
0.5235
0.6058
0.5607
0.5570
0.4535
0.7416
0.7104
1.3015
1.3111
0.9652
1.7947
1.8138
1.5669
1.5786
1.5126
1.7240
1.8334
2.7412
2.4335
2.6089
0.7507
0.6862
0.8747
0.7063
2.8797
1.7335
1.6422
1.8899
1.8790
1.0552
1.0092
1.9892
1.5569
1.0184
0.9971
1.4462
1.1078
2.2527
1.3718
1.2519
1.8771
2.3719
1.1474
1.6901
1.2372
3.5994
3.8248
3.4372
5.4177
1.6765
1.9426
3.8528
␶-torsion sub CH3 in Im
␶-torsion
␶-torsion
␶-torsion
␶-torsion
␶-torsion
␶-torsion of sub CH3 in Im
␶-torsion
␶-torsion of sub CH3 in Im
␶-torsion of sub CH3 in Im
␻-C7–C27 + ␻-C4–C35 + ␻-C5–C31
␻-C4–C35 + ␻-C5–C31
␻-C4–C35 + ␻-C5–C31 + ␻-C1–C16
␦-C4–C35 + ␦-C5–C31
␻-C–H of Ph1 and Im
␦-C4–C35 + ␦-C5–C31 + ␦-C7–C27
␦-C4–C35 ␦-C7–C27
␻-C–H of Ph1 and Im
␻-C–H of Ph1 + ␻-C1–C16
␻-C–H of Ph1 + ␻-C7–C27
␻-C C of Ph1 and Ph2
␻-C C of Ph1
␻-C C of Ph1 and Ph2
␳-C–H of Ph1
␻-C–H of Ph1
␻-C–HC–H of Ph2
␳-C C of Ph1
␳-C C of Ph1 and Ph2
␻-C–H of Ph1 and Ph2
Ring breathing of Ph1 and Ph2
Ring breathing of Ph1 and Ph2
␻-C4–C5–N3
Ring breathing of Im
␻-C C Ph2 + ␻-N2–C1–N3
␻-C C Ph1
106
114
131
163
188
216
227
251
259
276
286
299
319
332
357
372
386
420
441
444
446
534
554
560
575
609
620
630
657
679
718
730
751
761
781
803
875
880
890
895
938
977
978
993
995
998
1001
1012
1021
1021
1022
1043
1059
1073
1076
1080
1120
1131
1153
1158
1175
1197
1213
1224
1263
1297
1316
1324
109
116
133
164
189
217
225
250
258
272
286
300
319
332
358
373
388
422
443
445
448
537
558
562
577
611
622
632
659
684
723
735
753
765
781
800
877
880
894
895
938
968
978
992
994
997
1001
1002
1017
1024
1024
1038
1060
1073
1077
1083
1116
1130
1153
1155
1175
1194
1205
1215
1262
1298
1316
1325
64
76
101
139
152
168
193
231
247
280
289
309
335
352
364
405
405
408
430
492
509
559
572
581
616
621
643
655
676
700
702
741
782
792
802
813
813
816
910
921
928
931
937
961
967
983
986
999
1014
1018
1022
1075
1087
1093
1117
1133
1152
1181
1223
1228
1263
1270
1275
1281
1285
1328
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
␻-C C Ph1 + ␻-N2–C1–N3
␻-C–H of Im and Ph2
␦-C C of Ph1
␻-C–H of Ph2
␻-C–H of Ph1 + ring breathing of Ph2
␻-C–H of Ph1 and Ph2
␻-C–H of Ph1
␻-C–H of Ph1 and Ph2
␻-C–H of Ph2
␻-C–H of Ph1
␻-C–H of Ph1
␻-C–H of Ph2
(t)-C–H of Im
␦-C1–N2–C4
(t)-C–H of Ph1
␦-C C of Im and Ph2
␦-C C of Ph2
␳-C–H of Ph1
(t)-C–H of Im
␻-C–H of Ph1
␻-C–H of Im
␦-C–H of Ph2
␦-C–H of Ph1
Ring breathing of Ph2
␻-C–H of Im
␦-C–H of Ph2
␦-C–H of Ph1
␯-C7–C27 + ␦ C C of Ph1
␯-C–F + ␳-C–H of Ph2
␦-N2–C4–C5
␳-C–H of Ph2
␳-C–H of Ph1
␦-C C of Ph2
␳-C–H of Ph1
␦-N2–C1–N3
Ring deformation of Im (␯-C–N + ␯-C N)

146
J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
Table 9 (Continued )
SI. no
Calculated frequencies (cm−1
)
HF6-311G(d,p)
HF6-311G(d,p)
Vibrational assignment
B3LYP/6-31G(d,p)
HF/6-31G(d,p)
HF/6-311G(d,p)
Intensity
Activity
Reduced
mass
Force
constant
72
73
74
75
76
77
78
79
80
81
82
1355
1364
1370
1375
1384
1392
1423
1427
1434
1436
1438
1376
1389
1397
1409
1410
1427
1446
1455
1459
1462
1469
1374
1388
1394
1407
1408
1426
1445
1456
1459
1463
1510
10.1
31.9
4.7
3.2
0.3
22.1
24.9
4.4
3.6
7.9
3.7
14.8
3.2
15.4
3.4
40.2
34.8
4.8
2.2918
2.5204
2.2077
1.3907
1.2644
1.9456
1.9365
1.1861
1.1046
1.0495
1.1900
3.1112
3.4900
3.0861
1.9788
1.8040
2.8467
2.9075
1.8091
1.6901
1.6149
1.8475
␯-C6–N3
␯-C7–C27
␯-C4–C35
␯-C5–C31
␦-C–H of sub CH3 in Ph1
␯-C6–N3 + ␯-C1–N3
␦-C–H of sub CH3 in Im
␦-C–H of sub CH3 in Im
␦-C–H of sub CH3 in Ph1
␦-C–H of sub CH3 in Im
␦-C–H of sub CH3 in
Im + ␦-C–H of sub CH3 in Ph1
␦-C–H of sub CH3 in Im
␯-C1–N2
3.4
4.7
1.7
1.3
83
84
85
86
1439
1451
1488
1498
1469
1474
1512
1524
1521
1539
1559
1563
2.6
0.6
79.8
78.0
4.1
3.2
3.8
1.0693
1.1275
2.3822
3.3839
1.6608
1.7636
3.9061
5.6276
␯-C6–N3
␯-C C of
43.1
Ph2 + ␯-C1–N3 + ␯-C1–C16
␯-C C of Ph1 + ␯-C C of Im
␯-C C of Ph2 + ␯-C C of Im
␯-C C of Ph1 and
87
88
89
1554
1564
1568
1540
1563
1566
1598
1602
2792
6.4
8.1
2.4
6.8
1.5
1.5
5.7141
5.6598
5.4524
9.7293
9.8899
9.5793
Ph2+␯-C1–N2
90
91
92
93
94
95
96
97
98
1591
1593
2899
2904
2907
2945
2960
2962
2987
2988
2998
3038
3039
3061
3068
3068
3069
3083
3086
1601
1606
2787
2789
2791
2837
2840
2843
2846
2853
2856
2910
2911
2919
2923
2932
2944
2949
2950
2794
2843
2846
2853
2796
2836
2841
2843
2846
2853
2855
2910
2911
2918
2923
2932
2944
2948
2949
4.4
19.9
28.1
22.6
33.0
31.7
8.5
14.0
15.7
14.5
9.9
8.3
10.4
1.4
3.7
3.6
38.1
69.6
60.6
25.6
100.0
39.4
17.8
22.9
28.8
13.8
31.5
20.3
29.3
12.7
9.6
4.8182
5.1048
1.0357
1.0376
1.0376
1.1018
1.1009
1.1025
1.1034
1.1021
1.1019
1.0908
1.0912
1.0923
1.0917
1.0960
1.0945
1.0957
1.0954
8.8530
9.4180
5.8052
5.8242
5.8322
6.3750
6.3900
6.4096
6.4286
6.4508
6.4617
6.6426
6.6486
6.6903
6.7068
6.7754
6.8224
6.8486
6.8518
␯-C C of Ph1 and Ph2
␯-C C of Ph1 and Ph2
␯-C–H of sub CH3 in Im
␯-C–H of sub CH3 in Ph1
␯-C–H of sub CH3 in Im
␯-C–H of sub CH3 in Im
␯-C–H of sub CH3 in Im
␯-C–H of sub CH3 in Ph1
␯-C–H of sub CH3 in Im
␯-C–H of sub CH3 in Ph1
␯-C–H of sub CH3 in Im
␯-C–H of Ph1 (asym)
␯-C–H of Ph1 (asym)
␯-C–H of Ph1 (sym)
␯-C–H of Ph2 (asym)
␯-C–H of Ph1 (sym)
␯-C–H of Ph2 (asym)
␯-C–H of Ph2 (asym)
␯-C–H of Ph2 (sym)
99
100
101
102
103
104
105
106
107
108
20.4
28.1
30.1
61.0
4.4
3.3
4.2
␯ – stretching; ␤ – in-plane; ␥ – out-of-plane bending; ␻ – wagging; t – twisting; ␦ – scissoring; ␳ – rocking; ␶ – torsion. B – broad; S – strong; m – medium; w – weak. Scale
factors: 0.955 [B3LYP/6-31G(d,p)]; 0.8992 [HF/6-31G(d,p)]; 0.9051[HF/6-311G(d,p).
1380 cm−1 (1–6) is assigned to C C stretching mode. The calculated
wave number for this fundamental mode is around 1400 cm−1 by
B3LYP method.
[31]. In this region the bands are slightly affected by the nature of
the substituents. The scaled vibrations are around 2800 cm−1. The
experimental C–H vibrations are in good agreement with theoret-
ical vibrations.
3.7.5. Methyl group vibrations
The band at 2991 cm−1 is assigned to the CH3 asymmetric
stretching [36]. For the assignments of CH3 group frequencies one
can expect nine fundamentals to be associated with each CH3
group, viz., the symmetrical stretching in CH3 (CH3 sym. stretching),
asymmetrical stretching (i.e., in-plane hydrogen stretching mode),
the symmetrical (CH3 sym. deformation) and asymmetrical (CH3
asy. deformation) deformation modes, the in-plane rocking (CH3
ipr) and twisting t(CH3) modes. In addition to that CH3 ops, out-
of-plane stretch and CH3 opb, out-of-plane bending modes of the
CH3 group would be expected to be depolarized for asymmetry
species.
The C–H stretching in methyl group occurs at lower frequencies
than use of the aromatic ring (3100–3000 cm−1). The asymmet-
ric and symmetric stretching are observed around 2900 cm−1
are attributed to CH3 asymmetric stretching modes, theoretically
scaled values by B3LYP method around 3000 cm−1 assigned to
asymmetric stretching vibration. The scale down values 2900 cm−1
by B3LYP method for methyl symmetric stretching vibration shows
good agreement with the recorded FT-IR spectra. Very strong band
around 1030 cm−1 have assigned to CH3 asymmetric and sym-
3.7.3. C–N vibrations
The identification of the C–N vibration is a very difficult task
since mixing of several bands is possible in this region. Silver-
stein and Webster [30] assigned the C–N stretching absorption in
the region 1382–1266 cm−1 for aromatic amines. The C–N stretch-
ing mode is reported at 1368 cm−1 for benzamide [31], at 1382
and 1307 cm−1 for benzotriazole [32], at 1335, 1331 cm−1 for
2,4-dinitrophenylhydrimidazole [33] and at 1316 and 1213 cm−1
for morpholine-4-ylmethylthiourea [34]. In the present study, a
weak band observed in the spectra around 1228 cm−1 and these
frequencies are in good agreement with theoretically computed
values.
3.7.4. C C vibrations
The benzene ring possesses six stretching vibrations, of which
the four with the highest wave numbers occurring near 1600, 1580,
1490 and 1440 cm−1 are good group vibrations [35]. With heavy
substituents, the bands tend to shift to somewhat lower wave num-
bers and greater the number of substituents on the ring, broader the
absorption regions. In the present paper, the strong band around

J. Jayabharathi et al. / Spectrochimica Acta Part A 79 (2011) 137–147
147
Acknowledgments
One of the author Dr. J. Jayabharathi, associate professor in
chemistry, Annamalai University is thankful to Department of Sci-
ence and Technology [No. SR/S1/IC-07/2007] and University Grants
commission (F. No. 36-21/2008 (SR)) for providing fund to this
research work.
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