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.

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.

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.

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 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.

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.

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.

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, β_μ, 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.

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.

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.

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.

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.

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: v 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%.

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 least-squares method on F_obs² 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).

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 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.