A New Series of Bis (Thiosemicarbazone) Derivatives: Synthesis, Spectroscopic Characterization, and Antioxidant Activities

New bis (thiosemicarbazone) derivatives (1-5) were obtained from thiophene-2,5-dicarbaldehyde and numerous thiosemicarbazides. The thiosemicarbazides were prepared various isothiocyanates and hydrazine monohydrate. The structure elucidation of all obtained products were determined via routine spectroscopic techniques, including proton and carbon NMR (¹H, ¹³C), Fourier-transform infrared spectroscopy (FT-IR), and elemental composition analysis. In this research, the antioxidant activities of the newly synthesized compounds were assessed by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Based on the percentage of inhibition, the IC₅₀ values indicated the following order of activity: Trolox>1>3>4>2>5. Additionally, the reducing capabilities of the compounds were determined using the potassium ferricyanide reduction method. The absorbance values obtained from this assay for all the compounds were lower than that of Trolox, suggesting comparatively weaker reducing power. The study also explored how changes in molecular structure influence antioxidant activity, focusing especially on how various functional groups affect radical scavenging efficiency.