Synthesis and structural studies on (E)-3-(2,6-difluorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one: a promising nonlinear optical material

Abstract

A new fluorinated chalcone (E)-3-(2,6-difluorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one was synthesized in 90% yield and crystallized by a slow evaporation technique. Its full structural characterization and purity were determined by scanning electron microscopy, infrared spectroscopy, gas chromatography-mass spectrometry, ¹H, ¹³C and ¹⁹F nuclear magnetic resonance, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), Raman microspectroscopy, UV-Vis absorption spectroscopy, single crystal X-ray diffraction (XRD) and Hirshfeld surface (HS) analysis. The fluorinated chalcone crystallized in centrosymmetric space group P2₁/c stabilized by the C-H⋯O and C-H⋯F interactions and the π⋯π contact. The crystalline environment was simulated through the supermolecule approach where a bulk with 378 000 atoms was built. The electric parameters were calculated at the DFT/CAM-B3LYP/6-311++G(d,p) level as function of the electric field frequency. The macroscopic parameters such as linear refractive index and third-order nonlinear susceptibility (χ ⁽³⁾) were calculated, and the results were compared with experimental data obtained from the literature. The χ ⁽³⁾-value for the chalcone crystal is 369.294 × 10^-22 m² V^-2, higher than those obtained from a few similar types of molecule, showing that the chalcone crystal can be considered as a nonlinear optical material. Also, molecular theoretical calculations such as infrared spectrum assignments, frontier molecular orbital analysis and MEP were implemented, revealing that the most positive region is around the hydrogen atoms of the aromatic rings, and electrophilic attack occurs on the carbonyl group.

Fig. 1. Dipole moment as function of the iteration steps.

Scheme 1. Synthesis of FCH.

Fig. 2. (a) Single crystal photograph of FCH; (b) SEM micrograph of FCH.

Fig. 3. (a) TG/TGA and (b) UV-Vis absorption spectrum of FCH.

Fig. 4. Raman spectrum of FCH. Raman peak at 1032 cm⁻¹ was used to normalize the spectrum.

Fig. 5. ORTEP diagram for FCH. The ellipsoids are represented at 50% of probability level with the atomic numbering scheme. Hydrogen atoms are in arbitrary radii. Intramolecular interactions C8–H8⋯F2, C9–H9⋯F3 and C9–H9⋯O1 are represented.

Fig. 6. Representation of intermolecular interactions C5–H5⋯O1, C14–H14⋯F1 and C4–H4⋯F2.

Fig. 7. Hirshfeld surfaces plotted for FCH (a) C5–H5⋯O1 (1)/O1⋯H5–C5–F1 (2), (b) F1⋯H14–C14 (3)/C14–H14⋯F (4) and (c) C4–H4⋯F2 (5)/F2⋯H4–C4 (6). Dotted lines were used to represent hydrogen bonds.

Fig. 8. Shape index surfaces of (a) evidencing π⋯π interactions. Representation of π⋯π interactions (b).

Fig. 9. Fingerprint plots for FCH.

Fig. 10. Overlapping of X-ray geometric parameters (black) and theoretical calculation (green) structures for FCH.

Fig. 11. Frontier molecular orbitals for FCH (a) the HOMO “π” bonding orbital and (b) the LUMO “π” antibonding orbital derived from Kohn–Sham analysis at M062X/6-311++G(d,p) level of theory with the isovalue of 0.04 atomic units.

Fig. 12. The molecular electrostatic potential surface mapped for FCH. The red-colored region of the carbonyl group, and the blue-colored region around the hydrogen atoms. The density isovalue of 4.0 × 10⁻⁴ electrons per bohr³ was used to make the molecular electrostatic potential surfaces.

Fig. 13. The theoretical (red) and experimental (black) overlapped the FT-IR spectrum of FCH.

Fig. 14. Highlight of the rings A, B and C, with the atoms numbered as presented in Table 7.