Structural and nonlinear optical properties of cross-conjugated system benzophenone thiosemicarbazone: A vibrational spectroscopic study

Article abstract of DOI:10.1002/jrs.2788

The nonlinear optical (NLO) compound of interest benzophenone thiosemicarbazone (BTSC) was grown and the molecular structure generated with the aid of density functional theory (DFT). FT-Raman and IR spectra were recorded and analyzed. The harmonic wavenu

Full text of DOI:10.1002/jrs.2788

Research Article
Received: 14 April 2010
Accepted: 24 July 2010
Published online in Wiley Online Library: 27 September 2010
(wileyonlinelibrary.com) DOI 10.1002/jrs.2788
Structural and nonlinear optical properties
of cross-conjugated system benzophenone
thiosemicarbazone: a vibrational spectroscopic
study
C. Ravikumar and I. Hubert Joe∗
The nonlinear optical (NLO) compound of interest benzophenone thiosemicarbazone (BTSC) was grown and the molecular
structure generated with the aid of density functional theory (DFT). FT-Raman and IR spectra were recorded and analyzed.
The harmonic wavenumbers and IR and Raman intensities were computed with the B3LYP method. The observed vibrational
wavenumbers were compared with the calculated results. The assignments of the experimental spectra were made with the
help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field (SQMFF) methodology. The
electronic structure of the most important molecular fragments is described in terms of natural bond orbital (NBO) analysis.
c
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: conjugation; natural bond orbital (NBO) analysis; ICT; FT-IR; FT-Raman
Introduction
Experimental
Synthesis
Benzophenone derivatives show very interesting nonlinear op-
tical (NLO) activity as well as transparency, and the cross-
conjugated path in these molecular systems appear as a
powerful electronic system for the molecular engineering of
efficient second-harmonic generation (SHG) materials. A num-
ber of benzophenone derivatives show significantly high SHG
conversion efficiency.[1–3] The structure of the benzophe-
none molecule has been established on the basis of quan-
tum chemical calculations,[4] and vibrational wavenumbers
of benzophenone have been calculated.[5] The crystal struc-
tures of benzophenone[6] and benzophenone thiosemicarbazone
(BTSC)[7] have been reported. Thiosemicarbazones are pho-
tochromic materials and have attracted much attention be-
cause of their potential commercial value in applications such
as high-density information storage systems, photoswitching,
electro- or light-driven information display devices, and optical
calculation.[8,9] Vijayan and co-workers[10–13] have reported the
growth and characterization of some organic NLO semicarbazone
derivatives.
Vibrational spectroscopy is an efficient tool for the character-
ization of crystalline materials. It is effectively used to identify
functional groups and determining the molecular structure of
synthesized crystals. The present work deals with growth and
detailed vibrational spectral investigation of the crystal BTSC to
elucidate the correlation between the molecular structure and
NLO property, charge transfer interactions, and first hyperpolar-
izability, aided by using the scaled quantum mechanical force
field (SQMFF) technique based on density functional theory (DFT)
computation.
Benzophenone(99%Aldrich)andthiosemicarbazide(99%Aldrich)
were taken in 1 : 1 stoichiometric ratio and were dissolved in
ethanol. A few drops of H2SO4 were added as catalyst. The
prepared solution was slowly warmed till a clear solution was
obtained. The solution was kept in a covered container for
controlled evaporation. Good quality transparent crystals of BTSC
were obtained within a week.
Spectroscopic measurements
The UV–vis absorption spectrum of the sample was recorded in
acetone solution using a Varian–Cary 100 B10 UV–vis spectropho-
tometer. The Fourier transform infrared (FT-IR) spectrum of BTSC
was recorded in the region 4000–400 cm−1, with samples in KBr
pellets, using a Perkin Elmer RXI spectrometer. The resolution of
the spectrum is 4 cm−1. The NIR-FT Raman spectrum of BTSC in
the solid phase was recorded in the range 3500–50 cm−1 using
a Bruker RFS 100/S FT-Raman spectrophotometer with a 1064 nm
Nd : YAG laser source of 100 mW power. A liquid-nitrogen-cooled
Ge diode was used as the detector. The spectral resolution after
apodization was 2 cm−1
.
∗
Correspondenceto:I. Hubert Joe,CentreforMolecularandBiophysicsResearch,
Department of Physics, Mar Ivanios College, Thiruvananthapuram 695 015,
Kerala, India. E-mail: hubertjoe@gmail.com; hubertjoe@sancharnet.in
Centre for Molecular and Biophysics Research, Department of Physics, Mar
Ivanios College, Thiruvananthapuram695 015, Kerala, India
c
J. Raman Spectrosc. 2011, 42, 815–824
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

C. Ravikumar and I. H. Joe
procedure with MOLVIB and subsequently converted to relative
Raman intensities (Ii) using the following relationship derived from
the basic theory of Raman scattering[25,26]
:
f(ν0 − νi)4Si
ꢀ
ꢁ
ꢂꢃ
Ii =
(1)
−hcνi
νi 1 − exp
kT
where ν0 is the exciting wavenumber, νi is the vibrational
wavenumber of the ith normal mode, h, c, and k are universal
constants, and ‘f’ is a suitably chosen common scaling factor for
all the peak intensities. The simulated IR and Raman spectra were
plotted using pure Lorentzian band shapes with a full width at
half-maximum (FWHM) of 10 cm−1
.
The second-order polarizability or first hyperpolarizability β was
calculated using HF/6-31G∗ basis set on the basis of the finite-field
approach. The components of the first hyperpolarizability can be
calculated using the following equation:
Figure 1. Second-harmonic generation variation in BTSC for different
particle sizes as compared to urea: (a) 90 < r < 150 µm and (b) 150 < r <
180 µm.
βi = βiii + 1/3 ꢀ(βijj + βjij + βjji), (i = j)
(2)
Using the x, y, and z components, the magnitude of the first
hyperpolarizability tensor can be calculated by
SHG analysis
The SHG efficiency of the microcrystalline powders of BTSC
was examined by the powder reflection technique of Kurtz and
Perry.[14] Particlesizes(r),150 < r < 180 µmand90 < r < 150 µm,
graded using standard sieves were used for the measurement. A
Nd : YAG pulsed laser (1064 nm, 15 ns) beam was used. Ninety-five
percent of the beam was focused on the polycrystalline sample,
whiletheremaining 5%wasusedasareferencebeamtonormalize
the fluctuations of the incident laser. The second harmonic (SH)
radiation at 532 nm obtained at the output was filtered using
an SH separator to remove the fundamental input radiation.
The SH generated was detected by an RCA-931A photomultiplier
tube (PMT), which was connected to 100 MHz digital storage
oscilloscope (DSO). The change in the intensity of the SH as a
function of the fundamental was experimentally measured, and is
shown in Fig. 1. The SHG efficiency of BTSC was evaluated to be
on average 0.52 times that of urea.
1/2
β = (β2 + β2 + β2
)
z
(3)
x
y
The complete equation for calculating the magnitude of
first hyperpolarizability from Gaussian ‘98 W output is given as
follows[27]
:
β = [(βxxx + βxyy + βxzz)2 + (βyyy + βyzz + βyxx
+ (βzzz + βzxx + βzyy)2]1/2
)
2
(4)
To calculate the hyperpolarizability, the origin of the Cartesian
coordinate system was chosen as the center of mass of
the compound.[28] The components of the hyperpolarizability
tensor are shown in Table S1 (Supporting Information). The
calculated first hyperpolarizability of BTSC is 4.5 × 10−30 esu,
which is 23 times that of urea. The time-dependent density
functionaltheory(TD-DFT)methodwasusedtocalculateenergies,
oscillatorstrengthsofelectronicsinglet-singlettransitions, andthe
absorption wavelengths. Solvent effects were considered using
the polarizable continuum model (PCM) developed by Tomasi and
co-workers.[29–31]
Computational methods
The molecular geometry optimization and vibrational wavenum-
ber calculations of BTSC were performed by DFT method using the
Gaussian ‘98 package.[15] The Becke three-parameter hybrid ex-
change functional and the Lee–Yang–Parr correlation functional
(B3LYP) were utilized in the calculation with the 6-31G∗ basis set.
Nowadays, DFT calculations have been proved to be useful for
gaining insight into the structural properties of molecules.[16–19]
Normal coordinate analysis (NCA) was performed including the
calculation of vibrational modes and potential energy distribution
(PED) in local symmetry coordinates, as well as IR intensities and
Ramanactivitiescorrespondingtothescaledquantummechanical
(SQM) force field. These calculations were done with the MOLVIB
program version 7.0 written by Sundius.[20,21] Following the pro-
cedure of SQMFF, the harmonic force field for this compound was
evaluated and scaled at the B3LYP/6-31G∗ level of theory trans-
ferring the recommended scale factors of Rauhut and Pulay.[22,23]
Natural bond orbital (NBO) calculations of BTSC were performed at
the B3LYP/6-31G∗ level using the program NBO 3.1[24] included in
the Gaussian ‘98 program.[15] The Raman activities (Si) calculated
by Gaussian 98 program were suitably adjusted by the scaling
Results and Discussion
Optimized geometry
The optimized molecular structure of BTSC (Fig. 2) was calculated
using Gaussian ‘98 W program. The selected optimized geomet-
rical parameters are shown in Table 1. The thiosemicarbazone
moiety is nearly planar with the dihedral angle N24 –N25 –C26 –N27
(2.07◦) and adopts an E configuration with respect to the C7 N24
bond. In the benzophenone fragment, two phenyl rings are
nonplanar with C1 –C6 –C7 –C8 (−157.66◦) and C6 –C7 –C8 –C13
(−121.16◦) dihedral angles. The benzophenone and the thiosemi-
carbazone moieties are twisted, making the C1 –C6 –C7 –N24 and
C13 –C8 –C7 –N24 dihedralanglesof21.83◦ and59.40◦,respectively.
The more deviation in Ph2 region (C13 –C8 –C7 –N24) is due to the
steric repulsion between the H23 and H29 atoms. The C6 –C7 and
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2011, 42, 815–824

Structural and nonlinear optical properties of cross-conjugated system benzophenone thiosemicarbazone
distance (1.347 Å) is indicative of a slight double bond charac-
ter, suggesting extensive electron delocalization in the entire
· · ·
molecule. The short inter atomic distances H23 H29 (2.551 Å)
· · ·
and H29 S30 (2.729 Å) reveal the possibility of intramolecular
hydrogen bonding.
NBO analysis
NBOs provide the most accurate possible ‘natural Lewis structure’
picture of ψ, because all orbital details are mathematically chosen
to include the highest possible percentage of the electron
density (ED). A useful aspect of the NBO method is that it
provides information about interactions in both filled and virtual
orbital spaces that could enhance the analysis of intra- and
intermolecular interactions. These delocalization effects can thus
be depicted as a charge transfer from the highest occupied
bonding orbitals into unoccupied antibonding orbitals and their
importance can be more quantitatively characterized through
a second-order perturbative treatment that gives the energy
lowering associated with such interactions. The strength of the
delocalization interaction can be estimated by the second-order
energy lowering E(2)
:
Figure 2. Optimized structure of BTSC calculated at B3LYP/6-31G∗.
F(i, j)2
E(2) = ꢁEij = qi
(5)
εj − εi
C7 –C8 bond lengths are slightly larger than other C–C bonds, indi-
cating negligible conjugation interaction between the two phenyl
ring systems. The deviations of C6 –C7 –N24 (116.84◦), C8 –C7 –N24
(123.64◦), C7 –N24 –N25 (119.89◦), N24 –N25 –C26 (121.17◦), and
N25 –C26 –N27 (115.09◦) bond angles are due to the electronic
coupling between the amino nitrogen lone pair electrons and
the phenyl ring π system. The shortening of N24 –N25 (1.356 Å)
bond length indicates conjugation in the semicarbazone part. The
elongation of the predicted C–N bond lengths from the X-ray
data[7] suggests intense delocalization in the whole molecule. The
shortening of C–S bond length from the experimental results[7]
is due to its double bond character. Moreover, the C26 –N27 bond
where E(2) is the stabilization energy, qi is the donor orbital
occupancy, εi and εj are the diagonal elements (orbital energies),
and F(i, j) is the off-diagonal NBO Fock or Kohn–Sham matrix
element.[32]
Theintramolecularinteractionsareformedbytheorbitaloverlap
fromπ → π∗ bondorbitals, whichresultsinintramolecularcharge
transfer(ICT)causingstabilizationofthesystem.Theseinteractions
areobservedasanincreaseinED inC–Cantibonding orbitalwhich
weakens the respective bonds. The ED at the six conjugated π
bonds (∼1.65 e) and π∗ bonds (∼0.35 e) of the phenyl rings clearly
Table 1. Optimized geometrical parameters of BTSC based on B3LYP/6-31G∗ basis set
Bond length (Å)
Bond angle (◦)
Cal.
Dihedral angle (◦)
Cal.
Parameter
Cal.
Exp.a
Exp.b
Parameter
Exp.a
Parameter
Exp.a
0.55
C5 –C6
C6 –C7
C7 –C8
1.405
1.483
1.497
1.396
1.405
1.085
1.298
1.356
1.374
1.347
1.011
1.017
1.679
1.007
2.551
2.729
1.399
1.480
1.496
1.389
1.394
0.950
1.289
1.376
1.358
1.321
0.880
0.881
1.687
0.880
2.610
2.707
1.40
1.48
1.50
1.41
1.40
–
C1 –C2 –C3
120.32
119.54
120.79
119.52
119.80
120.13
119.64
116.84
123.64
119.89
121.17
115.09
120.08
122.11
120.19
120.32
120.42
119.70
120.44
118.97
119.82
120.39
119.96
116.70
124.31
117.43
119.70
116.70
120.01
120.14
118.58
119.99
C1 –C2 –C3 –C4
C2 –C3 –C4 –C5
C2 –C1 –C6 –C7
C4 –C5 –C6 –C7
C1 –C6 –C7 –C8
C6 –C7 –C8 –C13
C9 –C8 –C7 –N24
C5 –C6 –C7 –N24
C1 –C6 –C7 –N24
−0.05
−0.01
C2 –C3 –C4
−1.77
179.48
179.32
−148.16
−116.88
−115.68
−149.59
30.30
C5 –C6 –C7
−178.89
178.83
C12 –C13
C6 –C7 –C8
C8 –C13
C1 –H14
C7 –N24
C10 –C11 –C12
C11 –C12 –C13
C8 –C13 –H23
C6 –C7 –N24
C8 –C7 –N24
C7 –N24 –N25
N24 –N25 –C26
N25 –C26 –N27
C26 –N27 –H28
N24 –N25 –H29
N25 –C26 –S30
C26 –N27 –H31
−157.66
−121.16
−120.37
−157.47
21.83
–
N
24 –N25
25 –C26
–
N
–
C26 –N27
–
C13 –C8 –C7 –N24
C6 –C7 –N24 –N25
C8 –C7 –N24 –N25
C7 –N24 –N25 –C26
N24 –N25 –C26 –N27
N24 –N25 –C26 –S30
N25 –C26 –N27 –H31
59.40
−176.34
3.12
64.78
N
27 –H28
25 –H29
–
−177.67
0.71
N
–
C26 –S30
27 –H31
· · ·
–
−178.51
2.07
−172.27
−5.45
N
–
H23 H29
· · ·
–
−178.25
179.24
173.91
−179.95
H29 S30
–
a Taken from Ref. [7].
b Taken from Ref. [6].
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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C. Ravikumar and I. H. Joe
Table 2. Second-order perturbation theory analysis of Fock matrix in NBO basis
Donor (i)
ED(i) (e)
Acceptor (j)
ED(j) (e)
E(2)a (kJ mol−1
)
E(j) − E(i)b (arb. units)
F(i, j)c (arb. units)
π (C1 –C2)
1.670
π
∗ (C3 –C4)
∗ (C5 –C6)
∗ (C1 –C2)
∗ (C5 –C6)
∗ (C1 –C2)
∗ (C3 –C4)
∗ (C7 –N24
∗ (C7 –N24
∗ (C9 –C10
0.332
0.419
0.301
0.419
0.301
0.332
0.417
0.417
0.31
84.52
85.14
81.17
80.21
76.07
84.39
111.88
113.34
72.68
84.1
0.28
0.28
0.28
0.28
0.28
0.28
0.20
0.22
0.29
0.29
0.27
0.28
0.27
0.28
0.90
0.98
0.98
0.99
0.67
0.47
0.48
0.067
0.069
0.067
0.067
0.065
0.068
0.067
0.069
0.064
0.068
0.071
0.065
0.065
0.068
0.019
0.066
0.055
0.054
0.018
0.092
0.091
π
π
π
π
π
π
π
π
π
π
π
π
π
σ
σ
σ
σ
σ
σ
σ
π (C3 –C4)
π (C5 –C6)
1.657
1.626
)
)
π (C8 –C13
π (C9 –C10
)
)
1.630
)
∗ (C11 –C12
∗ (C8 –C13
∗ (C11 –C12
)
)
0.327
0.431
0.327
0.431
0.31
1.674
1.650
1.941
1.980
1.817
)
90.88
80.58
76.48
85.06
2.09
π (C11 –C12
n1(N24
)
∗ (C8 –C13
∗ (C9 –C10
∗ (C1 –H14
∗ (C7 –C8)
)
)
)
)
0.013
0.03
22.76
15.48
14.94
2.3
n1(S30
n2(S30
)
∗ (N25 –C26
∗ (C26 –N27
∗ (N24 –N25
∗ (N25 –C26
∗ (C26 –N27
)
)
0.108
0.084
0.015
0.108
0.084
)
)
)
92.34
85.52
)
ED, electron density.
a E(2) means energy of hyperconjugative interactions; cf Eqn (5).
b Energy difference between donor and acceptor i and j NBO orbitals.
c F(i, j) is the Fock matrix element between i and j NBO orbitals.
· · ·
Table 3. NBO results showing the formation of Lewis and non-Lewis orbitals by the valence hybrids corresponding to the intramolecular C–H
hydrogen bonds of BTSC
N
Bond (A–B)
σ (C7 –N24
ED (e)
1.977
Energy (kJ mol−1
)
EDA (%)
40.62
EDB (%)
59.38
NBO
S (%)
P (%)
)
−1856.12
0.6373 (sp2.92
)
25.48
31.69
31.71
28.69
29.40
32.37
30.45
100.0
41.78
26.82
39.43
74.44
68.20
68.25
71.21
70.52
67.58
69.47
–
C
+0.7706 (sp2.15
)
)
)
N
C
N
σ (N25 –C26
σ (C26 –N27
)
)
1.984
1.995
1.981
1.990
1.941
−1981.57
−1929.8
60.78
41.38
62.51
57.81
–
39.22
58.62
37.49
42.19
–
0.7796 (sp2.15
)
N
+0.6263 (sp2.48
0.6433 (sp2.40
)
C
+0.7656 (sp2.09
σ (C1 –H14
σ (C26 –S30
LP1(N24
)
−1353.92
−2304.14
−1062.28
0.7906 (sp2.28
+0.6123 (s)H
0.7603 (sp1.39
)
C
)
)
58.02
72.18
60.50
C
+0.6495 (sp2.69
)
S
)
sp1.53
demonstrates strong delocalization leading to a stabilization of
energy ∼83.06 kJ mol−1. The π electron cloud movement from
donor to acceptor can make the molecule highly polarized and
the ICT must be responsible for the NLO properties of BTSC. The
and sulfur atoms. The ED distribution around the imino group
mainly influences the polarity of the compound.
Mulliken charge analysis
orbital interaction energy between π(C8 –C13) → π∗ (C7 N24
)
and π(C5 –C6) → π∗ (C7 N24) are 113.34 and 111.88 kJ mol−1
,
The charge distribution on a molecule has a significant influence
of the vibrational spectra. The Mulliken atomic charges were
calculated at the B3LYP level using Gaussian ‘98, with the 6-
31G∗ atomic basis set. The chart in Fig. 3 shows the Mulliken
atomic net charges in BTSC. The atom N27 shows more negative
(−0.725 e) charge and C26 more positive (0.386 e) charge, which
suggests extensive charge delocalization in the entire molecule.
respectively (Table 2). These increases in the interaction energies
are due to the strong ICT interactions leading to the stabilization
of the molecule. According to NBO analysis (Table 3), all the CN
bond orbitals are polarized toward the nitrogen atom (68% at N),
whereas the C26 –S30 bond orbitals are polarized toward the sulfur
atom (72% at S). It is consistent with the charges on the nitrogen
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2011, 42, 815–824

Structural and nonlinear optical properties of cross-conjugated system benzophenone thiosemicarbazone
energies is due to the charge transfer interaction. NBO analysis
also shows the charge transfer interaction (explained earlier).
Vibrational spectral analysis
The vibrational spectral analysis of BTSC was made on the
basis of NCA. A non-redundant set of internal coordinates for
BTSC was defined (Tables S2 and S3), which was similar to
the ‘natural coordinates’ recommended by Pulay et al.[34] The
calculated wavenumbers were selectively scaled according to the
SQM procedure incorporating a set of eight transferable scale
factors (shown in the last column of Table S3) recommended
by Rauhut and Pulay.[22] The SQM wavenumbers related to the
observed bands are presented in Table 5 along with detailed
assignments. The observed FT-IR and Raman spectra as well as the
simulated theoretical spectra computed at B3LYP/6-31G∗ level are
given in Figs 5 and 6 for visual comparison.
Figure 3. Mulliken charge distribution of BTSC.
Phenyl ring vibrations
The shortening of the C26 –N27 bond (Table 1) also supports this
conclusion. The positive charges are localized on the hydrogen
atoms. Very similar values of positive charges are observed for the
hydrogenatomsbondedtothenitrogenatoms(H28,29,31 ∼0.361 e).
In the two phenyl rings, all the C atoms have negative charges
except C6 (0.12 e) and C8 (0.033 e), which suggests that the
electronic delocalization is more intense between the carbon
atoms responsible for charge transfer between the substituents.
The charge noticed on the N24 is smaller (compared to other N’s)
and equal to −0.312 e. This can be explained by high degree of
conjugation, with a strong push–pull effect between the imino
group and phenyl rings.[33]
The different normal vibrations of the monosubstituted phenyl
ringsareassignedaccordingtoWilson’snumberingconvention.[35]
There are five C–H stretching vibrations in monosubstituted ben-
zenes whose wavenumbers fall in the region 3120–3010 cm−1 [35]
.
The C–H stretching vibrations in the phenyl rings arises from two
nondegenerate modes a1g and b1u and two degenerate modes
e2g and e1u, i.e. vibrations 2, 13, 7, and 20 respectively. In mono-
substituted phenyl rings, 2, 7a, 7b, 20a, and 20b are active. The
medium intensity band in IR at 3147 cm−1 and the weak Raman
band at 3142 cm−1 are assigned to the 20a mode. The mode
20b is observed as strong Raman band at 3056 cm−1 and a weak
IR band at 3052 cm−1. From NCA, the mode 20b is predicted at
3054 cm−1 with strong Raman intensity (92.97). Normal mode 2
is observed as a weak band in IR at 3026 cm−1 and the mode 7a
is observed as weak bands at 2991 (IR) and 2992 cm−1 (Raman).
Several C–H stretching modes are found to be weak, which is due
to the charge transfer between the hydrogen atoms and carbon
atoms.[36] There are two doubly degenerate ring C–C stretching
modes e2g (8a, 8b) and e1u (19a, 19b) which are not perturbed
upon substitution.[37] Normal vibrations 8a, 8b, 19a, 19b, and 14
are categorized as C–C stretching vibrations. The mode 8a of the
Absorption spectra and solvent effects
The electronic spectrum of BTSC was computed in the gas phase
as well as in an ethanol environment and is listed in Table 4.
The solvent effect was calculated using PCM-TD-DFT method. The
observed and simulated (in gas phase and ethanol) UV–vis spectra
are shown in Fig. 4.
The n → π∗ transition energy is calculated at 406 cm−1, above
the experimental maximum in ethanol at 343 nm with strong
intensity. There are also two π → π∗ transitions. They are weak
and observed at 297 and 233 cm−1. The calculated absorption
wavelengths in ethanol at 363 and 320 nm are identified as
π → π∗ transitions. The red shift of the computed transition
monosubstituted ring is expected in the range 1614–1575 cm−1
,
and 8b extends from 1597 to 1562 cm−1. The normal mode 8a
is found at higher wavenumbers than 8b and appears simulta-
neously as strong IR and Raman bands at 1598 and 1589 cm−1
,
respectively. The enhanced intensity clearly exhibits the higher
Table 4. Calculated absorptions, energy, and oscillator strength of BTSC using TD-DFT method at B3LYP/6-31G∗ level
Gas phase
Ethanol
Wavelength (nm)
Excitation
Wavelength (nm)
Energy (eV)
Oscillator strength
Excitation
Cal.
Exp.
Energy (eV)
Oscillator strength
67 → 68
66 → 68
66 → 70
62 → 68
63 → 68
65 → 68
67 → 69
67 → 70
406.41
366.28
3.0507
3.3849
0.4934
0.0005
67 → 68
66 → 68
406.46
362.64
343
297
3.0503
3.4189
0.5020
0.0004
319.76
3.8774
0.0051
65 → 68
67 → 70
67 → 72
320.21
233
3.8720
0.0033
c
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2011, 42, 815–824
wileyonlinelibrary.com/journal/jrs

C. Ravikumar and I. H. Joe
Figure 4. (a) Experimental UV–vis spectrum of the BTSC molecule in ethanol solvent. (b) Simulated UV–vis spectrum of the BTSC molecule in the gas
phase. (c) Simulated UV–vis spectrum in ethanol for BTSC molecule calculated with the TD-DFT/PCM method.
Figure 6. (a) FT-Raman spectrum of the BTSCmolecule in the wavenumber
range 3500–50 cm−1. (b) Simulated Raman spectra of the BTSC molecule
computed at B3LYP/6-31G∗ basis set.
Figure 5. (a) FT-IR spectrum of the BTSC molecule in the wavenumber
range 4000–400 cm−1. (b) Simulated IR spectra of the BTSC molecule
computed at B3LYP/6-31G∗ basis set.
degree of the conjugation between the two rings.[38] The ring
mode 8b for Ph2 is observed only in Raman as a strong band
at 1570 cm−1. The 19a mode in monosubstituted benzene can
be expected near 1500 cm−1 with higher intensity, and 19b ap-
in both IR and Raman of modes 8a and 14 evidences the charge
transfer interactions.[36,38,39] The normal modes 3, 9a, 15, 18a, and
18b are classified as C–H in-plane bending vibrations. The bands
observed at 1283 cm−1 in IR is assigned to the mode 3 of Ph1,
and those at 1274 cm−1 (IR) and 1276 cm−1 (Raman) are assigned
to the mode 3 of Ph2. The vibrational mode 9a is observed as a
weak band in IR at 1161 cm−1. The mode 15 is coupled with the
ring C–C stretching coordinate and found to be active in IR at
1152 cm−1 as a strong band. The very strong predicted intensities
(126.64 (IR) and 161.83 (Raman)) of mode 15 is correlated with
the experimental intensities. The mode 18b is observed as strong
band in IR at 1067 cm−1, and the mode 18a occurs as a strong
band in IR at 1026 cm−1 and in Raman at 1027 cm−1 as weak band.
The C–H out-of-plane bending (5, 10a, 10b, 11, and 17a), radial
skeletal (1, 12, 6a, and 6b), and the out-of-plane skeletal (4,16a,
and 16b) vibrations are listed in Table 5.
pears as weak band around 1470 cm .
−1 [35] This vibration 19 has a
faint C–H in-plane bending nature with hydrogen and its carbon
moving in opposite directions. The mode 19a appears as a strong
band in IR at 1473 cm−1. According to PED calculation, vibrational
mode 19a has only 25% C–C stretching contribution and 39%
C–H in-plane bending character. The weak band that appears at
1464 cm−1 in Raman is assigned to the 19b mode of Ph1 and the
weak band in IR at 1400 cm−1 is assigned to 19b of Ph2. In Ph1,
the ring mode 14 is observed as a medium intensity band in IR
at 1323 cm−1 and its counterpart in Raman occurs as a strong
band at 1328 cm−1. The bands observed at 1305 and 1308 cm−1
in IR and Raman, respectively, are assigned to the mode 14 of Ph2.
The simultaneous appearance of the ring C–C stretching bands
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2011, 42, 815–824

Structural and nonlinear optical properties of cross-conjugated system benzophenone thiosemicarbazone
Table 5. Vibrational assignment of BTSC by normal mode analysis based on SQM force field calculations
Observed
fundamentals (cm−1
)
Selective scaled B3LYP/6-31G∗ force field
νIR
νRaman
νi (cm−1
)
Ai IRa
Ii Rb
Assignment with PED (%)c
3410 m
–
3480
3378
3340
3082
3076
3076
3068
3067
3061
3054
3054
3048
3046
1589
1584
1580
1567
1556
1547
1462
1452
1448
1409
1404
1401
1297
1289
1280
1268
1254
1249
1157
1139
1137
1119
1117
1083
1053
1052
1042
1008
1006
980
101.06
29.53
52.25
7.07
67.49
268.11
75.18
113.71
150.22
288.24
21.24
189.8
85.62
164.84
92.97
16.97
42.13
55.7
NH2as (94)
3345 m
3347 w
νNH (99)
3238 m
3241 vw
νNH2ss (93)
20aνCHph1 (99)
3147 m
3142 w
–
–
17.72
13.48
20.98
34.13
11.86
11.16
0.85
νCHph1 (98)
–
–
νCHph2 (98)
–
–
νCHph2 (99)
–
–
–
νCHph1 (99)
–
νCHph2 (99)
–
–
νCHph1 (97)
20bνCHph2 (98)
2νCHph2 (99)
7aνCHph1 (99)
3052 w
3026 w
2991 vw
1598 s
–
3056 s
–
1.13
2992 w
1.36
1589 vvs
83.97
153.98
1.67
8aνCCar1 (29), NH2sci (23), νCN (20)
NH2sci (46), νCCar1 (24), νCN (14)
νCCar2 (66), δR2CH (19), R2symd (10)
νCCar1 (33), νCN (18), CCCrock (14)
8bνCCar2 (58), δR2CH (15), νCCar1 (11)
νCN (35), νCCar1 (31), δR1CH (10)
NHrock (31), νCN (19), δR1CH (15), νCCar1 (11)
δR2CH (39), 19aνCCar2 (25)
δR1CH (31), 19bνCCar1 (19), δR2CH (16), NHrock (12)
νCN (30), δR1CH (22), νCCar1 (18)
δR1CH (25), νCCar1 (20), νCN (19), δR2CH (11)
δR2CH (37), 19bνCCar2 (28), νCN (20)
14νCCar1 (76), δR1CH (13)
14νCCar2 (72), δR2CH (24)
νCC (28), δCCN (21), δR2CH (12), δR1CH (10)
3δR1CH (48), δR2CH (15)
–
74.55
94.83
1327.07
6.94
–
–
–
–
24.51
1.8
–
1570 vs
–
–
27.41
383.65
109.04
176.83
34.51
45.06
63.2
1300.29
259.54
45.93
20.22
81.3
1497 w
1473 vs
–
1498 m
–
1464 w
1438 s
–
1446 m
–
5.73
1400 w
1323 m
1305 w
–
–
18.57
14.53
6.69
1328 s
1.49
1308 m
2.32
–
70.73
9
291.85
7.01
1283 sh
1274 m
1200 sh
1170 s
–
–
1276 w
81.09
214.01
38.48
4.12
56.04
127.71
26.2
3δR2CH (27), νCCar2 (25), NH2rock (10)
NHrock (17), νCC (15), NH2rock (14)
νCC (21), νNN (19)
–
1174 m
–
6.84
δR2CH (78), νCCar2 (17)
–
1161 w
12.36
0.02
45.24
5.51
9aδR1CH (74), νCCar1 (15)
15δR2CH (87), νCCar2 (13)
δR1CH (87), νCCar1 (12)
1152 s
–
–
–
0.3
12.82
161.83
6.89
1085 s
–
1091 s
126.64
14.93
9.77
νNN (36), δCCN (14)
–
νCCar1 (38), δR1CH (37)
1067 s
1049 s
1026 vs
1000 sh
–
–
0.85
νCCar2 (39), 18bδR2CH (37)
νCN (32), NH2rock (16), δCNN (11)
νCCar1 (48), 18aδR1CH (19), νCCar2 (17)
νCCar2 (43), νCCar1 (18), δR2CH (16), 12R2trigd (12)
R2trigd (46), νCCar2 (27), R1trigd(18)
12R1trigd (48), νCCar1 (25), R2trigd (14), νCCar2 (12)
Car2Hwag (84), R2puck (14)
5Car1Hwag (83), R1puck (15)
Car2Hwag (90)
–
26.26
8.02
3.74
1027 w
4.41
1001 s
5.06
21.75
27.48
108.53
0.73
–
2.58
970 m
–
–
980
0.35
–
968
0.23
944 m
–
945 w
964
0.09
1.89
–
941
0.46
1.78
930 m
922 w
–
–
938
0.81
1.54
17aCar1Hwag (90)
–
923
13.72
1.73
23.66
2.61
17aCar2Hwag (32), δCCN (13), νCCar1 (12)
Car1Hwag (66), Car2Hwag (14)
10bCar2Hwag (45), 10bCar1Hwag (17)
Car2Hwag (98)
–
901
888 w
–
–
–
897
5.77
3.38
833
0.94
7.07
845 vs
848 vs
826
20.71
5.99
10aCar1Hwag (60), νC S (10)
c
J. Raman Spectrosc. 2011, 42, 815–824
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C. Ravikumar and I. H. Joe
Table 5. (Continued)
Observed
fundamentals (cm−1
)
Selective scaled B3LYP/6-31G∗ force field
νIR
νRaman
νi (cm−1
)
Ai IRa
Ii Rb
Assignment with PED (%)c
–
–
825
760
753
713
682
672
644
634
627
613
607
590
578
537
482
470
447
408
393
387
342
285
257
241
214
190
178
133
72
47.11
18.27
18.7
3.79
32.54
20.63
3.18
13.93
13.27
0.04
0.3
35.46
3.27
3.47
3.92
3.23
3.54
3.78
5.63
1.57
7.96
3.48
1.52
2.52
5.77
12.15
4.54
0.75
3.38
2.17
3.92
2.1
Car1Hwag (32), νC S (16)
775 vs
779 w
10aCar2Hwag (28), R2puck (18), Car2Cwag (15), Car1Hwag (13)
Car1Hwag (31), R1puck (17), Car1Cwag (13)
11Car2Hwag (19), R2symd (18), νCC (14)
4R2puck (46), Car2Hwag (33), Car2Cwag (10)
4R1puck (49), Car1Hwag (30), Car1Cwag (11)
R1puck (22),-Ph1-C-Ph2-t (18)
–
–
724 m
729 w
698 vs
–
671 s
–
675 vw
650 vw
–
–
R2puck (23), R1asymd (12), N–C Swag (11)
R2puck (18), N–C Swag (16), CNH2t (12)
R1symd (59), R1asymd (16)
–
619 w
–
–
–
599 vw
6bR2asymd (64)
–
–
2.41
10.46
66.81
1.71
5.54
25.87
5.72
0.05
0.8
CCCrock (36), δCCN (24), R2symd (11)
N–C Swag (53), CNH2t (36)
–
–
–
535 vw
CNH2t (25), N25Ct (23), NHwag (22), N24Nt (17)
16bR2symt (20), Car2Cwag (11), Car1Cwag (10), R1asymt (10)
16aR1asymt (16),-Ph1-C-Ph2-t (15), Car1Cwag (12)
R2symt (20),-Ph1-C-Ph2-t (16), Car2Cwag (13), δCNN (10)
N–C Srock (36)
–
499 m
–
481 vw
–
433 w
–
412 w
–
–
R1symt (49), R1asymt (18), bCar1H (15), R2asymt (12)
16aR2asymt (64), Car2Hwag (13)
–
364 w
–
–
10.82
5.32
8.24
5
C7Nt (34), R1asymt (13)
–
268 m
1.36
1.52
4.1
CCCrock (24), δCar1C (14), δCCN (10)
R2symt (29), δCCN (21)
–
–
–
225 w
δNNC (21), νCC (20)
–
–
54.14
47.69
95.87
2.24
0.36
0.37
0.53
0.27
0.1
6.36
1.51
2.29
4.45
7.86
6.06
4.67
14.91
2.39
2.29
CNH2wag (17), δCar2C (16), R1asymt (13)
CNH2wag (24), δCar2C (13), δCCN (12)
CNH2wag (40)
–
197 w
–
–
–
100 vs
-Ph1-C-Ph2-t (53), NHwag (10)
–
–
–
–
–
–
–
CCCrock (47), δCCN (25)
–
61
C8C7t (31), Car2Cwag (21), N25Ct (10)
–
57
N
24Nt (23)
C6C7t (46), C8C7t (22)
25Ct (24), C8C7t (24), NHwag (15), CNH2wag (12), C7Nt (10)
-Ph1-C-Ph2-t (57), C8C7t (19), C6C7t (18)
–
53
–
43
N
–
29
0.31
The notations in superscripts are as depicted in the study by Varsanyi.[35]
vs, very strong; vvs, very very strong; s, strong; m, medium; sh, shoulder; w, weak; vw, very weak; R/ph/ar, phenyl ring; ν, stretching; ss, symmetric
stretching; as, asymmetric stretching; b, δ, bending; t, torsion; sci, scissoring; wag, wagging; rock, rocking; trigd, trigonal deformation; symd, symmetric
deformation; asymd, asymmetric deformation; symt, symmetric torsion; asymt, asymmetric torsion; puck, puckering.
a Calculated IR intensities.
b Relative Raman intensities normalized to 100 cf Eqn (1).
c Only PED values greater than 10% are given.
NH2 and NH vibrations
in-plane bending mode 3 to give a medium intensity band at
1274 cm−1 in IR and a weak band at 1276 cm−1 in Raman. The NH2
out-of-plane vibrations are shown in Table 5. The bands appearing
at 3345 cm−1 (IR) and 3347 cm−1 (Raman) are assigned to the N–H
stretching mode. The N–H in-plane bending mode is observed as
a medium intensity band in Raman at 1498 cm−1 and as a weak
band in IR at 1497 cm−1. The NH stretching wavenumber is in
good agreement with the PED (99%) results.
The NH2 stretching vibrations of thioamides occur near 3380 and
3180 cm−1 forasymmetricandsymmetricstretchingvibrations.[40]
The asymmetric NH2 stretching is observed as a medium band in IR
at3410 cm−1.Thebandsat3238 cm−1 (IR)and3241 cm−1 (Raman)
are assigned to symmetrical NH2 stretching mode. The blue shift of
the NH2 stretching wavenumbers is due to the formation of inter-
· · ·
and intramolecular N–H N hydrogen bonds. The NH2 scissoring
that appears as strong bands at 1598 cm−1 in the IR spectrum
and 1589 cm−1 in Raman has 23% of NH2 bending character
because of its association with 8a and CN stretching modes. The
NH2 rocking mode is coupled with ring C–C stretching and C–H
ꢂC N–N–C≺ vibrations
In phenyl-substituted hydrazones, the possibility of obtaining a
charge transfer interaction is related to the absence of even a
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
J. Raman Spectrosc. 2011, 42, 815–824

Structural and nonlinear optical properties of cross-conjugated system benzophenone thiosemicarbazone
shown in Fig. 7. The HOMO–LUMO difference is 2.48 eV. The
above results show that BTSC crystal is the best material for NLO
applications.
Conclusion
The BTSC crystals were grown by the slow evaporation technique.
The calculated first hyperpolarizability of BTSC is found to be
4.5 × 10−30 esu, which is 23 times that of urea. Kurtz and
Perry powder reflection studies confirm the second-order NLO
properties of the molecule. The optimized geometry shows that
the two phenyl rings are nonplanar. The simultaneous occurrence
of modes 8a and 14 provide evidence for the charge transfer
interactions. The enhanced intensity of mode 8a clearly shows the
higher degree of conjugation, which is responsible for the optical
nonlinearity of the crystal. The red shift of the C S stretching
wavenumber confirms the greater contribution of resonance form
ꢂN+ C–S−. The elongation of the C–N bond length and the
downshifting of C N stretching wavenumber clearly bear out the
charge transfer interaction between the phenyl rings through the
ꢂ-N C-≺ skeleton. The shortening of the N–N bond observed in
semicarbazone,whichhasanextensivelydelocalizedgrouponN25,
confirms that the compound is a delocalized and conjugated one.
Figure 7. (a) HOMO plot of BTSC at B3LYP/6-31G∗. (b) LUMO plot of BTSC
at B3LYP/6-31G∗.
slight amount of strain in the hydrazono group, which must
be perfectly planar to allow conjugation of the group.[38] The
C
N stretching modes of thiosemicarbazones occur in the
region 1655–1642 cm−1 [40]
.
The C N stretching vibrations are
coupled with the ring C–C stretching modes. The strong bands
observed at1598 and 1589 cm−1 in IR and Raman, respectively, are
assigned to the C N stretching mode. The downshifting of C
N
stretching wavenumber and the enhanced intensity are due to
the charge transfer interaction between the phenyl rings through
the
skeleton.[38] The N–N stretching mode
Supporting information
is observed as a medium intensity band at 1085 cm−1 (IR) and
at 1091 cm−1 (Raman). The CNN bending vibration is prominent
along with the ring C–H out-of-plane bending 17a and ring C–C
Supporting information may be found in the online version of this
article.
stretching modes and seen as a weak band in IR at 922 cm−1
.
References
C
S vibrations
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S stretching wavenumbers can be attributed to the greater
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and LUMO (−5.46 eV) energies indicate a charge delocalization
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J. Raman Spectrosc. 2011, 42, 815–824
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/jrs

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