A comprehensive study on the photophysical and non-linear optical properties of thienyl-chalcone derivatives

The impact of the substitutional position of the chorine atom on the non-linear optical (NLO) response of chalcone derivatives is reported in this paper. Two thienyl-chalcone derivatives, (E)-3-(2,4-dichloro-phenyl)-1-(2,5-dichlorothiophen-3-yl)prop-2-en-1-one (3A25D2) and (E)-3-(2,6-dichloro-phenyl)-1-(2,5-dichlorothiophen-3-yl)prop-2-en-1-one (3A25D4), are synthesized, and their crystal structures were determined by single-crystal X-ray diffraction analysis. The photophysical and third-order NLO properties of 3A25D2 and 3A25D4 were investigated experimentally and computationally. The third-order NLO properties of 3A25D2 and 3A25D4 dissolved in N,N-dimethylformamide (DMF) were studied using Z-scan technique with 800 nm, 70 femtosecond (fs) pulses, and 532 nm continuous wave (CW) laser excitation. Closed aperture data recorded with fs pulses revealed positive non-linearity of both the compounds, while a strong negative non-linearity was observed in the CW regime. Open aperture data revealed that both the compounds exhibit positive non-linear absorption in fs pulsed and CW domains. Several wave function analysis methods, such as the inter-fragment charge transfer (IFCT) analysis, hole-electron analysis, (hyper)polarizability density analysis, and decomposition of the (hyper)polarizability contribution by numerical integration, were carried out to study the optical properties and charge transfer mechanism. In addition, the influence of the medium (liquid and crystalline) and external field wavelength on the optical properties of the two molecules were analyzed. Thermal and electronic contributions toward NLO properties were studied experimentally. The theoretically calculated cubic hyperpolarizability γ(-ω; ω, ω, -ω) in liquid for 3A25D2 and 3A25D4 were 4.69 × 10^-34 and 2.68 × 10^-34 esu, whereas the corresponding femtosecond regime Z-scan results gave 4.35 × 10^-34 and 3.78 × 10^-34 esu, respectively.