Molecular structure, linear optical, second and third-order nonlinear optical properties of two non-centrosymmetric thiophene-chalcone derivatives

Two chalcones, (2E)-1-(5 bromothiophen-2-yl)-3-(3-fluorophenyl) prop-2-en-1-one (3F5B2SC) and (2E)-1-(5-bromothiophen-2-yl)-3-(4- methoxyphenyl) prop-2-en-1-one (4M5B2SC) were synthesised and crystallized by slow evaporation solution growth technique to investigate their structural, linear optical, thermal and nonlinear optical properties. Initially, the structures of 3F5B2SC and 4M5B2SC were confirmed by FT-IR and NMR (H-1 and C-13 NMR) spectroscopic studies. Detail solid state structures of these grown crystals were determined by single crystal XRD data analysis. Both the chalcones are crystallized in the non-centrosymmetric monoclinic crystal system. The thermal analysis (DSC, TGA, DTA and DTG) revealed that 3F5B2SC and 4M5B2SC molecules are thermally stable upto their melting points for solid state studies. The linear optical properties of these chalcones were studied in the UV-Vis-NIR region. The estimated direct energy band gap of the molecules by Tauc's plot (4.7 eV for 3F5B2SC and 4.2 eV for 4M5B2SC) are comparable with HOMO-LUMO gaps. The MEP and NBO of both the molecules are studied by DFT method. The second harmonic generation (SHG) efficiency of 4M5B2SC and 3F5B2SC determined by Kurtz-Perry powder method is found to be 5.3 and 4.2 times that of urea, respectively. Third-order NLO parameters, such as nonlinear absorption coefficient (beta= similar to 10(-4) cm/W), nonlinear refractive index (n(2) = similar to 10(-9) cm(2)/W), susceptibility (chi((3)) =similar to 10(-7) esu) and molecular hyperpolarizability (gamma(h) = similar to 10(-27) esu) were determined unambiguously from Z-scan experimental data analysis. The molecules exhibited optical limiting behaviour for continuous wave (CW) laser operating at 532 nm wavelength. Computationally, the dipole moment, static and dynamic polarizability and hyperpolarizability of both the chalcones were determined by TD-DFT and TD-HF method. The obtained results suggest that the studied thiophene-chalcones may be used in optical device as frequency generator, optical limiter and optical switch. (C) 2020 Elsevier B.V. All rights reserved.