Studies on structural, optical, thermal and vibrational properties of thienyl chalcone derivative: 1-(4-Nitrophenyl)-3-(2-thienyl)prop-2-en-1-one

Abstract The structural, optical, thermal and vibrational properties of thienyl chalcone derivative 1-(4-Nitrophenyl)-3-(2-thienyl)prop-2-en-1-one, C 13 H 9 NO 3 S were investigated combining nuclear magnetic resonance ( 1 H and 13 C NMR), X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV–vis spectroscopy at room temperature assisted by density functional theory (DFT) calculations and Raman scattering at the temperature range 303–463 K. The electronic properties, including excitation energies, oscillator strengths, HOMO and LUMO energies were calculated by time-dependent DFT (TD-DFT) to complement the experimental findings. The B3LYP/6-311G (d,p) (B3LYP/cc-pVTZ) calculations led to the identification of ‘two minima on the molecules’ potential energy surfaces. From these calculations, it was predicted that the most stable conformer for C 13 H 9 NO 3 S in the gas phase is founded at 0 K relationship to dihedral angle C8 C9 C10 S1, in agreement with XRD results. The molecular plot showed that the electrical charge mobility in the molecule occurs from thiophene to benzene ring. The optical band gap energy calculated from the difference between HOMO and LUMO orbitals was founded to be ∼3.87 (3.82) eV, in close agreement with the experimental value of 2.94 eV. The comparison between experimental and theoretical vibrational spectra gives a precise knowledge of the fundamental vibrational modes and leads to a better interpretation of the experimental Raman and infrared spectra. As temperature increases from room temperature to 443 K, it was observed the current phonon anharmonicity effects associated to changes in the Raman line intensities, line-widths and red-shift, in special in the external modes region, whereas the internal modes region remains almost unchanged due its strong chemical bonds. Furthermore, C 13 H 9 NO 3 S goes to phase transition in the temperature range 453–463 K. This thermal phenomenon was attributed to the disappearance of the lattice (∼10-200 cm −1 ) and molecular (∼300-4000 cm −1 ) modes in the Raman spectra. Finally, the vibrational mode assignment given in terms of potential energy distribution (PED) analysis leads to a more comprehensive interpretation of the vibrational spectra and origin of instability the investigated material.