<p>Thioamides play an important role in peptide chemistry and therapeutic applications, especially as intermediates in organic synthesis and heterocycle formation. In this study, novel thioamide derivatives were synthesized using Schiff bases derived from the reactions of 4-aminoindane and 5-aminoindane with substituted benzaldehydes. The structures of all synthesized molecules were confirmed by ¹H NMR, ¹³C NMR, FT-IR, and ESI–MS. Antioxidant activities were assessed using DPPH and iron chelation assays, with IC₅₀ values determined. The antifungal and antibacterial properties of the thioamides were examined using the well diffusion method, and minimum inhibitory concentration (MIC99) was determined via the microdilution method. Although the molecules demonstrated moderate antioxidant activity, significant antibacterial effects were observed, especially against <i>Pseudomonas aeruginosa</i> and <i>Bacillus subtilis</i>. Most of the molecules exhibited strong antifungal and biofilm-inhibiting activity, particularly <i>N</i>-(2,3-dihydro-1<i>H</i>-inden-5-yl)-2-hydroxy-3-methoxybenzothioamide, which displayed broad-spectrum activity against both Gram-negative and Gram-positive bacteria. The findings suggest a positive structure–activity relationship for molecules with the same core structure but different substituents.</p> Graphical abstract <p></p>