Research Journal of Recent Sciences ________________________________________________ ISSN 2277 - 2502
Vol. 1(ISC-2011), 337-340 (2012)
Res.J.Recent.Sci.

Short Communication

Crystal structure optimization, Semi-empirical quantum chemical
calculations and Non-linear optical property of a thiazolo
[3, 2-a] pyrimidine derivative
Jotani Mukesh M.,1 and Baldaniya Bharat B.,2
1

Physics Department, Bhavan’s Sheth R. A. College of Science, Khanpur, Ahmedabad, Gujarat,INDIA
2
Chemistry Department, M. G. Science Institute, Navrangpura, Ahmedabad, Gujarat, INDIA

Available online at: www.isca.in
(Received 15th November 2011, revised 31th December 2011, accepted 24th January 2012)

Abstract
The crystal structure of the title molecule has been analyzed with the help of AM1 semi-empirical calculations to explain the crystal
packing effect and the results were compared with earlier DFT analysis. The electric dipole moment ( ) and static first and second
order hyperpolarizabilities ( and ) have been computed using Time Dependent Hartree Fock (TDHF) method incorporated in
MOPAC2009 program to inspect the microscopic non-linear optical behaviour of the title compound. This is in good agreement
with the experimentally measured second harmonic generation efficiency of the compound which is 0.36 and 4.17 times to those of
urea and KDP respectively, hence it suggests the non-linear optical behaviour of the material. The intramolecular charge transfer
interactions result during the HOMO-LUMO transitions observed from the calculated energy values.
Keywords: Second harmonic generation, dipole moment, hyperpolarizabilty, non-linear optical property.

Introduction
The non-linear optics finds large intersection with
experimental and theoretical physics, chemistry and
engineering. It has attracted considerable interest not only
due to its application in electro-optics, telecommunication
etc., but also due to the fundamental research associated with
charge transfer interaction, conjugation, polarisation and
crystallization of material into non-centrosymmetric lattice.
The material with which a light can exhibit non-linear optical
(NLO) property is primarily controlled by its various order
non-linear succeptibilities.

dihydro-5H-[1,3] thiazolo [3,2-a] pyrimidine-6-carboxylate
crystallized into non-centrosymmetric lattice may possess
NLO behaviour. The crystallographic details along with the
influence of different interactions on crystal packing effects
have been discussed and published earlier1.

The crucial distinction between traditional materials and
recent organic materials is revealed during the analysis of the
origin of their non-linear succeptibilities. The large optical
succeptibility, ultra fast response time and high optical
threshold for organic materials compared to traditional
materials like urea, potassium dihydrogen phosphate (KDP),
theorem lead to the study of organic NLO materials.
The intrinsic properties to be optimized and compared for the
NLO activity of the material at microscopic level are dipole
moment () and hyperpolarizabilities ( and ).
From the crystal structural study on a series of
pharmaceutically important thiazolo [3, 2-a] pyrimidine
compounds designed to ascertain the influence of
substitution pattern on crystal packing, the title compound,
Ethyl (2Z,5R)-2-benzylidene-7-methyl-3-oxo-5-phenyl-2,3International Science Congress Association

Figure- 1
Molecular structure with Atom labelling scheme
Figure 1 shows the molecular structure with atom labelling
scheme. The present work relates the molecular structural
features, hyperpolarizabilities and NLO response of material
with the special emphasis on the role of intramolecular
charge transfer mechanism in such a structure using HOMOLUMO studies.

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Research Journal of Recent Sciences ____________________________________________________________ ISSN 2277 - 2502
Vol. 1(ISC-2011), 337-340 (2012)
Res.J.Recent.Sci

Material and Methods
Second harmonic generation efficiency measurement:The
non-linear optical second harmonic generation efficiency of
microcrystals was measured by Kurtz-Perry powder SHG
method at Indian Institute of Science, Banglore, and India2.
A Q-switched nanosecond pulsed (8 ns, 10Hz) Nd:YAG
laser beam of 1064 nm wavelength and 5.6 ml power is used
for the measurement. The grown single crystals of the
compound were ground with particle size in the range 100ked in a microcapillary of uniform bore. The
input laser beam was allowed to pass through the sample
after reflection from the infra red reflector and the output
from the sample was filtered by monochromator to separate
the fundamental from the SHG signal. The second harmonic
generated by randomly oriented microcrystals was focussed
by a lens and detected by photomultiplier tube (Hammatsu
RS 109). The emission of green light from the sample
confirmed second harmonic generation. The crystalline
powdered samples of urea and potassium dehydrogenate
phosphate (KDP) with the same size as that of title
compound is used as a reference.
Semi-empirical quantum chemical calculations: Austin
Model 1 (AM1) is one of the popular semi-empirical
methods for the calculation of electronic molecular
properties such as ground state geometry, molecular energy
and molecular polarizability. Austin Model 1 together with
the restricted Hartree Fock closed shell wave function was
used to perform semi-empirical quantum chemical
calculations in order to optimize the experimental structure
and to calculate hyperpolarizabilities using MOPAC2009
program3.
The minimizations were terminated at r. m. s. gradient less
than 0.01 kJ mol-1 Å-1 and optimized geometry together with
dipolemoment vector is shown in figure 2. The comparision
of the geometries optimized by density functional theory
(DFT) and MOPAC2009 with the geometry observed from
the crystal structure is given in table 1. The geometrically
optimized molecule is then used to compute the static values using time dependent Hartree Fock (TDHF) method
incorporated in MOPAC2009 program.
vec, the vector component along dipole moment at zero
frequency is defined as

β vec 

3 β μ
5 μ

(1)

Where

β  μ  β x μ x +β yμ y +βzμ z

And

βi =βiii +βijj +βikk ……(3)
2

2

2

β tot =[β x +β y +β z ]1/2

(2)

(4)

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Here,tot and vec are determined from the computed
sensorial components. Due to 3D nature of molecule, Klein
man symmetry relations and the squared norm of Cartesian
expressions for  tensor were taken into account while
calculating vec and tot. The calculated  and  for the title
molecule are given in table 2.

Figure-2
AM1 optimized molecule Showing dipole moment vector

Results and discussion
The semi-empirical AM1 calculated values for the optimized
geometry together with DFT calculated and experimental
values are listed in Table 1. The comparison of C-N-C and
C-C-N bond angles for the fused thiazolopyrimidine system
between experimental values (crystallographic information
file), DFT and semi-empirical AM1 calculated values with
small deviations confirm the screw-boat conformation of
puckered pyramiding ring. The shortening of C = O distance
between C8 and O3 atoms from the optimized geometrical
value and the significant difference in the torsional angle
around C3-C8 and O2-C9 bonds may be due to the
involvement of these atoms in the intramolecular C-H…O
and C-O… interactions.
The semi-empirical AM1 calculations also support presence
of intermolecular C-H…S interaction characterized by C6C17-C18-C19 torsional angle (9.8(4) ° (cif); 15.72° (AM1).
The discrepancies in the bond distances and some other
geometrical parameters between AM1 calculated and
experimental values are also observed similar to that with
DFT calculated model.
Thus semi-empirical quantum
chemical calculations also support the crystal packing
interaction of title molecule. The TDHF calculations
indicates that the three dimensional molecule possess no
symmetry and has a point group C1.
The second harmonic generation resulted from the randomly
oriented microcrystals in a micro capillary tube through the
emission of a green light of wave length 532 nm. The output
of SHG signal generated from the title compound was
measured as 100 mV in comparison with 24 mV and 274 mV
outputs measured for the reference compounds KDP and urea

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Research Journal of Recent Sciences ____________________________________________________________ ISSN 2277 - 2502
Vol. 1(ISC-2011), 337-340 (2012)
Res.J.Recent.Sci
respectively. Thus, the title compound has SHG efficiency
equals 4.17 and 0.36 times to that of KDP and urea
respectively.
The
dipole
moment
()
and
hyperpolarizabilities ( and ) calculated by TDHF method
are given in Table 2. The dipole moment vector is aligned
diagonally across bc -plane of unit cell and normal to the
plane extending to acetyl group on one side and to the
benzene ring through C=C group on other side of the central
fused pyrimidine system Which is shown in figure 1. The
larger magnitude of dipole moment () is due to the effective
charge separation within the molecule.
The large first order hyperpolarizability () compared to that
of urea also suggest non-linear optical behavior of the
material in the solid state. The measure of non-linear optical
response of a molecule tot has the dominance of vec and oct
both given in table 2. In addition the third order
hyperpolarizability ()has also significant contribution to
the non-linear optical property due to its relatively large
value.

excited state is described by one electron transition from
highest occupied molecular orbital (HOMO) to lowest
unoccupied molecular orbital (LUMO). The frontier
molecular orbital HOMO is localized with the large
concentration around the atoms of central fused pyrimidine
system shown in figure 3, whereas LUMO is located near
the most of the coplanar atoms including benzylidene moiety
of the molecule (figure 4). An electron transition from
HOMO to LUMO through an absorption of energy equal to
homo-lumo energy gap equals to7.323 eV reflects the
chemical activity of a molecule thereby resulting
intermolecular charge transfer between the atoms of the
molecule.

Conclusion
The optimized geometry of title molecule using DFT and
AM1 semi-empirical computations reveals the involvement
of atoms in short intermolecular C-H…S, C-H…O and CO…interactions for the crystalline environment of the
molecule. The dipole moment and hyperpolarizabilities have
been computed by TDHF method from AM1 optimized
geometry of the molecule using MOPAC2009 program. The
computed value suggest the non-linear optical behaviour of
the material at microscopic level and is supported by the
experimental SHG efficiency measurements. The dipole
moment vector () aligned diagonally across bc-plane of unit
cell has large magnitude. The intramolecular charge transfer
results within the atoms of molecule during HOMO-LUMO
transition.

Acknowledgements
Figure- 3
Homo composition of molecular orbital

The authors are thankful to Indian Institute of Science,
Banglore, India for powder SHG measurement.

References
1. Jotani M.M., Baldaniya B.B. and Jasinski J.P., Crystal
Structure of Ethyl (2Z, 5R)-2-benzylidene-7- methyl-3oxo-5-phenyl-2, 3-dihydro-5H-[1,3] Thiazolo [3,2-a]
Pyrimidine-6-carboxylate, J. Chem. Crystallogr., 39,
898-901 (2009)
2. Kurtz S.K. and Perry T.T., J. Appl. Phys., 39, 37983813 (1968)
3. Stewart J.P., MOPAC2009, Stewart Computational
Chemistry, Version 8.351w web:http://OpenMOPAC.net
Figure-4
Lumo composition of molecular orbital
The semi-empirical quantum chemical calculations using
MOPAC2009 are also employed to compute the different
form of energies such as heat of formation, transition
energies, ionization potential etc. These values are listed in
Table 3. The analysis of restricted Hartree Fock wave
function indicates that the transition from ground to first

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4. Suenaga M. Facio version 14.1.1 Computational
Chemistry environment for MOPAC, GAMES and
GAUSSIAN
5. Allouche A. R., Gabedit, A graphical user interface for
Computational Chemistry, J. of Comp. Chem.,
Doi:10.1002/jcc.21600, (2010)

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Research Journal of Recent Sciences ____________________________________________________________ ISSN 2277 - 2502
Vol. 1(ISC-2011), 337-340 (2012)
Res.J.Recent.Sci

Bond
O2-C8
O2-C9
O3-C8
C9-C10
Bonds
C1-N2-C5
C2-N2-C5
N2-C2-C3
N2-C1-N1
Bonds
C8-O2-C9-C10
C4-C3-C8-O3

Table-1
Selected geometrical parameters
(a) Bond lengths (Å)
Experimental (cif) DFT calculated
1.332(2)
1.387
1.451(4)
1.485
1.184(3)
1.236
1.404(5)
1.530
(b) Bond angles (°)
Experimental (cif) DFT calculated
116.65(19)
118.42
123.33(17)
121.72
108.29(17)
108.48
126.9(2)
126.55
(c) Torsional angles (°)
Experimental (cif) DFT calculated
115.0(4)
78.57
11.4(3)
3.01

AM1 calculated
1.371
1.435
1.237
1.509
AM1 calculated
114.30
125.73
110.61
125.68
AM1 calculated
80.29
19.52

Table-2
Dipolemoment and hyperpolarizabilities

x
- 0.291
x
-16.513
tot
27.092

(a) Dipolemoment (D)
y
 z

-3.750
- 1.455
4.033
(b) First order hyperpolarizabity (× 10 -30 esu)
 y
z

-21.363
-2.223
 vec
oct

16.26
10.23
(c) Second order hyperpolarizabity (× 10 -35 esu)
av = 9.2869
Table-3
Energy values from Semi-empirical calculations

Heat of formation
Total energy
Electronic Energy
Core-Core repulsion
No of filled levels
Ionization potential
Homo-Lumo energies

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0.987 Kcal /mol (4.129 KJ)
-4787.552 eV
-38163.892 eV
33376.340 eV
73
8.666 eV
-8.666 eV, - 1.343 eV.

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