Synthesis, crystal structure, spectra and quantum chemical study on 1-phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline

Article abstract of DOI:10.3390/molecules19045313

1-Phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline was synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction. UV-Vis spectra and fluorescence spectra were measured. Density functional theory calculations on the structure of the title compound were performed at the B3LYP/6-311Glevel of theory. NPA atomic charge distributions indicate that, although the S atom in the thienyl ring loses coordination capacity, the title compound still may be used as a potential multi-dentate ligand to coordinate with metallic ions. The calculation of the second order optical nonlinearity was carried out. Natural bond orbital analyses indicate that the electronic absorption bands are mainly derived from the contribution of n ? pand p ? ptransitions. Fluorescence spectra determination shows that the title compound is a potential orange-light emitting material.

Full text of DOI:10.3390/molecules19045313

Molecules 2014, 19, 5313-5324; doi:10.3390/molecules19045313
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molecules
ISSN 1420-3049
www.mdpi.org/molecules
Article
Synthesis, Crystal Structure, Spectra and Quantum Chemical
Study on 1-Phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline
Huan-Mei Guo 1,*, Pu-Su Zhao 2, Qian Wu 1 and Yu-Feng Li 1
1
Microscale Science Institute, Weifang College, Weifang 261061, China;
E-Mails: wuqianwq2006@163.com (Q.W.); liyufeng8111@163.com (Y.-F.L.)
2
Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials, Huaiyin Normal University,
Huaian 223300, China; E-Mail: zhaopusu@hytc.edu.cn
* Author to whom correspondence should be addressed; E-Mail: huanmeiguo@163.com;
Tel.: +86-536-878-5283; Fax: +86-536-878-5802.
Received: 24 March 2014; in revised form: 14 April 2014 / Accepted: 17 April 2014 /
Published: 23 April 2014
Abstract: 1-Phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline was synthesized and
characterized by elemental analysis, IR and X-ray single crystal diffraction. UV-Vis
spectra and fluorescence spectra were measured. Density functional theory calculations on
the structure of the title compound were performed at the B3LYP/6-311G** level of theory.
NPA atomic charge distributions indicate that, although the S atom in the thienyl ring loses
coordination capacity, the title compound still may be used as a potential multi-dentate
ligand to coordinate with metallic ions. The calculation of the second order optical
nonlinearity was carried out. Natural bond orbital analyses indicate that the electronic
absorption bands are mainly derived from the contribution of n → π* and π → π*
transitions. Fluorescence spectra determination shows that the title compound is a potential
orange-light emitting material.
Keywords: synthesis; crystal structure; spectra; DFT; second order optical nonlinearity
1. Introduction
Pyrazoline derivatives are five-membered, nitrogen-containing heterocyclic compounds with high
hole-transport efficiency, excellent blue emission and high quantum yield [1–3], which have made
them useful as fluorescent brightening agents, fluorescence chemosensors, hole-transport materials in

Molecules 2014, 19
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electrophotography, OLED and as fluorescent materials [4–8]. Since 2001, different groups have
prepared pyrazoline nanoparticles ranging from tens to hundreds of nanometers in size by using the
re-precipitation method and explored their size-tunable optical properties for application in
optoelectronic devices [9–11]. Our group has also reported the synthesis, structure and spectra
properties of a series of 2-pyrazolines by experimental and theoretical methods [12–18].
Among numerous pyrazoline derivatives, one type of pyrazolines containing thienyl groups has
been proved very important. For example, they can be introduced at the C-4 position of a
1,8-naphthalimide derivative and lead to stronger fluorescence emission [19]. Various synthetic
methods for this type of pyrazolines have been reported, such as a microwave method [20], a catalytic
method in the present of base [21] a refluxing method [22], and so on.
On the other hand, with the development of theoretical chemistry, density functional theory (DFT)
has become an increasingly useful tool to compare and verify experimental studies. The success of
DFT is mainly due to the fact that it describes small molecules more reliably than Hartree-Fock theory.
It is also computationally more economic than wave function based methods with inclusion of electron
correlation [23,24].
However, to our knowledge, no structural data obtained either by experimental or theoretical methods
have been reported so far for the title compound, 1-phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline,
which contains both a pyrazolinyl and a substituted thienyl group. Thus, in order to characterize the
correlation between molecular structure and macroscopic properties in the studied compound,
it seemed essential to undertake a detailed comparative study of the isolated molecule and the solid
state unit. In this paper, after the title compound was synthesized by a refluxing method
(see Scheme 1), a concerted approach by X-ray crystallography and DFT calculations was used, which
takes advantage of both the high interpretative power of the theoretical studies and the precision and
reliability of the experimental method. We hope that the research presented herein will be helpful for
the design of pyrazoline-based electroluminescent devices and materials.
Scheme 1. Synthetic route to the title compound.
O
N
O
O
O
O
N
Acetic acid
Reflux
+
NHNH2
N
N
C CH CH
S
H
S
2. Results and Discussion
2.1. Description of the Crystal Structure
The displacement ellipsoid plot with the numbering scheme for the title compound is shown in
Figure 1. Figure 2 shows a perspective view of the crystal packing in the unit cell. Selected bond
lengths and bond angles by X-ray diffractions are listed in Table 1 along with the calculated
bond parameters.

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Figure 1. Molecular structure with the atomic numbering scheme for the title compound.
5315
Figure 2. A view of the crystal packing down the c axis for the title compound.
The molecular structure of the title compound consists of discrete [PhC3HN2PhNO2C4H3S] entities.
All of the bond lengths and bond angles in the phenyl rings are in the normal range. In the pyrazolinyl
ring of the molecule, the C=N bond length [1.332(4) Å] is longer than that in the similar structure
[C=N 1.297(2) Å] [25]. The bond lengths of C–N [1.365(4) Å] and N–N [1.356(3) Å] are shorter than
those found in the above-cited structure [C–N 1.474(2) Å, N–N 1.380(2) Å] [25]. The pyrazolinyl ring
makes dihedral angles of 5.39(3), 60.10(3) and 19.27(11), respectively, with the p-nitrophenyl,
phenyl and 2-thienyl rings.

Molecules 2014, 19
Table 1. Selected structural parameters by X-ray and theoretical calculations.
5316
B3LYP/
6-311G**
1.730
B3LYP/
6-311G**
1.457
Bond Lengths (Å) Experiment
Bond Lengths (Å) Experiment
S(1)–C(13)
S(1)–C(10)
1.675(5)
1.704(3)
1.201(6)
1.225(6)
1.356(3)
1.365(4)
1.430(4)
1.332(4)
1.480(5)
1.374(4)
C(1)–C(10)
C(2)–C(3)
1.458(4)
1.402(4)
1.466(4)
1.389(5)
1.393(5)
1.381(5)
1.402(5)
1.373(4)
1.381(5)
1.362(5)
1.750
1.415
O(1)–N(3)
1.225
C(3)–C(4)
1.468
O(2)–N(3)
1.225
C(4)–C(5)
1.403
N(1)–N(2)
1.348
C(4)–C(9)
1.405
N(1)–C(1)
1.380
C(5)–C(6)
1.387
N(1)–C(14)
1.429
C(10)–C(11)
1.373
N(2)–C(3)
1.334
C(14)–C(19)
1.394
N(3)–C(7)
1.474
C(15)–C(16)
1.391
C(1)–C(2)
1.383
C(17)–C(18)
1.394
Bond Angles (°)
C(13)–S(1)–C(10)
N(2)–N(1)–C(1)
C(3)–N(2)–N(1)
O(1)–N(3)–O(2)
N(1)–C(1)–C(2)
C(1)–C(2)–C(3)
N(2)–C(3)–C(2)
C(5)–C(4)–C(9)
Bond Angles (°)
C(8)–C(7)–C(6)
C(11)–C(10)–S(1)
C(10)–C(11)–C(12)
C(13)–C(12)–C(11)
C(12)–C(13)–S(1)
C(19)–C(14)–C(15)
C(17)–C(16)–C(15)
C(17)–C(18)–C(19)
92.7(2)
112.0(2)
105.4(2)
125.1(5)
105.8(2)
106.2(3)
110.6(3)
117.9(3)
91.6
121.6(4)
109.6(2)
111.4(4)
113.4(4)
112.9(3)
121.0(3)
120.5(3)
119.9(3)
121.6
110.5
112.9
113.3
111.7
120.6
120.3
120.4
111.9
106.0
124.6
105.8
105.7
110.6
118.7
In the crystal lattice, there are two intermolecular interactions (C–H···Y, Y=N) [26,27] and some
C–H···π supramolecular interactions (see Table 2) [28]. In the solid state, all above supramolecular
interactions stabilize the crystal structures.
Table 2. Hydrogen bonds and C–H···π supramolecular interactions a.
D–H···A
Symmetry
x, 1 − y, −1/2 + z
−x, −y, −z
H···A (Å) D···A (Å)
∠D–H···A (°)
176.98
135.30
134
C(13)–H(13)···N(2)
C(19)–H(19)···O(1)
C(11)–H(11)···Cg(4)
C(16)–H(16)···Cg(4)
C(18)–H(18)···Cg(1)
2.510(3)
2.552(2)
3.037(1)
3.209(2)
2.809(2)
3.439(3)
3.279(1)
3.743(1)
3.879(3)
3.596(2)
x, y, z
1/2 − x, 1/2 + y, 1/2 − z
131
1/2 − x, 1/2 − y, −z
143
a Cg(1) and Cg(4) denote thienyl ring and phenyl ring C(14)–C(19), respectively.
2.2. Optimized Geometry
DFT calculations were performed on the title compound at B3LYP/6–311G** level of theory. Some
optimized geometric parameters are also listed in Table 1. In view of the bond lengths in Table 1, most
predicted values are longer than experimental ones and the biggest difference between the theoretical
and experimental values occurs at S(1)–C(13) bond, with the different values being 0.0554 Å. As for the
bond angles, most predicted values correspond with the experimental values and the biggest difference
is seen in the bond angle of C(12)–C(13)–S(1), with a difference between values of 1.22°. The reasons for
the above discrepances maybe as follows: (1) the theoretical values correspond to the isolated

Molecules 2014, 19
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molecule in the gas-phase and the experimental values are from the molecule in the solid state.
The geometry of the solid-state structures is subject to intermolecular forces, such as van der Waals
interactions and crystal packing forces, which make most of the experimental bond lengths shorter than
the theoretical ones; (2) in the solid state, there exists a C–H···π supramolecular interaction
corresponding with the thienyl ring (see Table 2), while in theoretical calculations, supramolecular
interactions are neglected, which, to some extent, may lead to bigger bond length and bond angle
differences between the experiments and calculations corresponding to the thienyl ring. Despite of
some differences, the DFT method used here can reproduce the molecular geometry on the whole and
it is the basis for our following discussion.
2.3. Atomic Charge Distributions
Based on B3LYP/6-311G** optimized geometry, NPA atomic charge distributions of the title
compound were calculated. All of the atomic charges of non-hydrogen atoms are listed in Table 3.
Table 3. NPA atomic charge distributions obtained at B3LYP/6-311G** level.
Atom
N(1)
N(2)
C(1)
C(2)
C(3)
N(3)
O(1)
O(2)
Charges (e)
−0.16920
−0.28191
0.13219
Atom
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
S(1)
Charges (e)
−0.03329
−0.18105
−0.17616
0.05712
Atom
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
Charges (e)
−0.22313
−0.24353
−0.37017
0.14793
−0.27626
0.13913
−0.17632
−0.16957
0.41951
−0.19406
−0.18771
−0.19584
−0.18649
−0.20411
0.51394
−0.38790
−0.38977
C(10)
−0.22371
As seen from Table 3, all non-hydrogen atomic charge distributions are not only influenced by the
atomic electronegativity, but also by the conjugation mode around the atom. For example, for the
nineteen C atoms, there are three atomic charge distribution phenomena: (1) in the two phenyl rings
and one thienyl ring, because C atoms have higher electronegativity than H atoms, thirteen C atoms
conjugated with H atoms have negative atomic charges; (2) since the electronegativity of C is smaller
than that of N, four C atoms joined with N atoms have positive atomic charges; (3) for the C(4) and
C(10) atoms, they are indirectly conjugated with the N atoms, which makes them have negative atomic
charges. In addition, for three N atoms, N(1) and N(2) atoms are connected with C atoms, so they both
carry negative atomic charges. However, for the N(3) atom, there are two O atoms and one C atom
bond with it, which leads the N(3) atom to have a positive charge. It is remarkable that, although the S
atom has higher electronegativity than the C atoms, in the thienyl ring, the atomic charge values of S
are positive, indicating that this S atom loses the capacity to coordinate with metallic ions, which is
very different from that in a free thiophene molecule. On the whole, considering the atomic charge
distributions and the steric effect, the title compound has three sites, namely N(2), O(1) and O(3),
which have negative charge values and allow it to act as a multi-dentate ligand to coordinate with
metallic ions.

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2.4. Calculations of Nonlinear Optical Property
Since 2-pyrazoline derivatives have non-linear optical (NLO) properties [29], so we also made a
prediction on the title compound. The predicted results were compared with the traditional NLO
materials of urea and para-nitroaniline (PNA). On the basis of the MNDO Hamiltonian and PM3
parametrization with the MOPAC program package, the molecular hyperpolarizability value, βμ,
the vector components along the dipole moment direction, of the title compound were calculated to be
4.997 × 10−30 esu, which is greater than the value of urea (0.14 × 10−30 esu calculated using the same
method) [30] and smaller than that of PNA (6.801 × 10−30 esu calculated using the same method).
The comparisons indicate that the title compound is a potential NLO material.
2.5. Electronic Absorption Spectra
The electronic absorption spectrum of the title compound have been measured in EtOH solution and
is shown in Figure 3. From Figure 3, one can find that there are four electronic transition peaks and
three of them locate at about 208, 244 and 265 nm, respectively, which are in the ultraviolet region
range. The fourth peak is at 434 nm, indicating the title compound solution has absorbed the
blue-light and led to the solution being yellow.
Figure 3. Electronic absorption spectra of the title compound measured in EtOH solution.
434 nm
208 nm
244 nm
265 nm
1.0
0.5
0.0
200
300
400
500
600
Wavelength(nm)
Natural population analyses based on the B3LYP/6-311G** optimized geometry show that the
frontier molecular orbitals of the title compound are mainly composed of p atomic orbitals, so
electronic transitions corresponding to above electronic spectra are mainly assigned to n → π* and
π → π* electronic transitions. Figure 4 shows the surfaces of the HOMO-1, HOMO, LUMO and
LUMO+1 for the title compound. As seen in Figure 4, when electron transitions take place, electrons
are mainly transferred among the phenyl ring, nitrophenyl ring and thienyl ring, they correspond to the
n → π* and π → π* electronic transitions.

Molecules 2014, 19
Figure 4. Some frontier molecular orbital stereographs for the title compound.
5319
LUMO
LUMO+1
HOMO
2.6. Fluorescence Spectra
HOMO-1
The solid-state fluorescence spectrum of the title compound is shown in Figure 5. The spectrum
exhibits two weak emissions at 425 and 487 nm, respectively, which are in the violet-light region.
A maximum emission band is at 604 nm, which is in the orange-light region. This result suggests the
title compound is a potential orange-light emitting material.
Figure 5. Solid-state fluorescence spectra of the title compound.
604 nm
10
5
425 nm
487 nm
0
400
500
Wavelength(nm)
600
700

Molecules 2014, 19
5320
3. Experimental and Theoretical Methods
3.1. Physical Measurements
Elemental analyses for carbon, hydrogen and nitrogen were performed by a Perkin-Elmer 240C
elemental instrument. IR spectra (4000–400 cm−1) were recorded on a Nicolet FT-IR spectrophotometer
as KBr pellets. Electronic absorption spectra were measured on a Shimadzu UV3100 instrument in
EtOH solution and solid-state fluorescence spectra were measured on a F96-fluorospectrophotometer.
3.2. Synthesis
All chemicals were obtained from a commercial source and used without further purification.
1-(4-Nitrophenyl)-3-(2-thienyl)-2-propenyl-1-ketone (0.01 mol) and phenylhydrazine (0.015 mol)
were mixed in acetic acid (40 mL) and stirred during reflux for 6 h. Then, the mixture was poured into
ice-water to afford light-yellow solids. The solids were filtered and washed with water until the pH of
the solution was about 7. Finally, the light-yellow solid crystals of the title compound were dried at
room temperature. Yield 78.6%. Mp. 168.1–169.2. IR: ν 3433(m), 3055(m), 1588(vs), 1550(s),
1492(vs), 1390(s), 1338(vs), 1267(m), 1127(s), 1107(s), 1062(m), 1034(w), 992(m), 839(s), 742(vs),
710(m), 685(s), 512(w) cm−1. Found: C, 65.51; H, 3.89; N, 12.23%. Calc. for C19H13N3O2S: C, 65.69,
H, 3.77, N, 12.10%.
3.3. Crystallographic Study
The selected crystal of the title compound was mounted on an Rigaku raxis Rapid IP Area Detector
diffractometer. Reflection data were measured at 293(2) K using graphite monochromated Mo-Kα
(λ = 0.71073 Å) radiation and a ωscan mode. The correction for Lp factors and empirical absorption
were applied to the data. The structures were solved by direct methods and refined by full-matrix
2
least-squares method on Fobs using the SHELXTL software package [31]. All non-H atoms were
anisotropically refined. The hydrogen atom positions were fixed geometrically at calculated distances
and allowed to ride on the parent C atoms. The final least-square cycle gave R = 0.0707, wR2 = 0.1922.
Atomic scattering factors and anomalous dispersion corrections were taken from International Table for
X-ray Crystallography [32]. A summary of the key crystallographic information is given in Table 4.
CCDC-990511 contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: +44(0)1222-336033; E-Mail: deposit@ccdc.cam.ac.uk).
3.4. Computational Methods
Initial molecular geometry of the title compound was taken from its crystal structure. Then, DFT
calculations at B3LYP/6-311G** levelof theory by the Berny method [33] were performed with the
Gaussian 03 software package [34]. Vibrational frequencies calculated ascertain the structure was
stable (no imaginary frequencies). Natural Bond Orbital (NBO) analyses were also performed on the
optimized structure. On the basis of the MNDO Hamiltonian [35] and PM3 parametrization [36] with

Molecules 2014, 19
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the MOPAC [37] program package, the molecular hyperpolarizability value was also calculated. All
calculations were performed on a DELL PE 2850 server and a Pentium IV computer using the default
convergence criteria.
Table 4. Summary of crystallographic results for the title compound.
Empirical Formula
Formula weight
C19H13N3O2S
347.38
Temperature
293(2) K
Wavelength
0.71073 Å
Crystal system, space group
Unit cell dimensions
Monoclinic, C2/c
a = 28.023(7) Å
b = 7.8005(15) Å β = 122.69(2)°
c = 18.008(7) Å
Volume
3312.9(17) Å3
Z, Calculated density
Absorption coefficient
F(000)
8, 1.393 Mg/m3
0.213 mm−1
1440
θ range for data collection
Limiting indices
3.26 to 25.00°
−33 ≤ h ≤ 33, −9 ≤ k ≤ 8, −21 ≤ l ≤ 21
10,658/2887 [Rint = 0.0476 ]
Full-matrix least-squares on F2
2887/0/226
Reflections collected/unique
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R indices (all data)
1.120
R1 = 0.0707, wR2 = 0.1922
R1 = 0.0911, wR2 = 0.2071
0.402 and −0.404 e. Å−3
Largest diff. peak and hole
4. Conclusions
1-Phenyl-3-(4-nitrophenyl)-5-(2-thienyl)-2-pyrazoline has been synthesized and characterized, by a
variety of methods including IR, X-ray single crystal diffraction, UV-Vis and fluorescence
spectroscopy. For the title compound, DFT calculations at B3LYP/6-311G** of the structure and NPA
atomic charge distributions have been carried out. Experimental and predicted results indicate that the
optimized geometry at B3LYP/6-311G** level can represent the molecular structure. NPA atomic
charge distributions show the title compound may be acted as multi-dentate ligand to coordinate with
metallic ions. The electronic absorption spectra measurement of the title compound exhibits four
absorption bands and DFT calculations indicate the above electronic spectra are mainly assigned to
n → π* and π → π* electronic transitions. The solid-state fluorescence spectrum reveals the title
compound is a potential orange-light emitting material.
Acknowledgments
This work was supported by Fund of Jiangsu Key Laboratory for Chemistry of Low-Dimensional
Materials (JSKC12107 and JSKC12106) and Huaian Science & Technology Bureau, Jiangsu Province,
China (HAG2012005, HAG2013009 and HC201307).

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Author Contributions
Huan-Mei Guo for synthesis and writing the manuscript; Pu-Su Zhao for calculations and analysis;
Qian Wu for characterizations of the title compound; Yu-Feng Li for single crystal structural refinement.
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Sample of the title compound is available from authors.
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