<p>A simple fluorescent sensor, 1,5-bis(2,4-dihydroxyphenylmethylene)thiocarbohydrazone (H₆L), was designed for the selective detection of sodium ions amidst other cations. The molecular structure of H₆L was confirmed using the SCXRD method, which reveals significant hydrogen bonding interactions in the lattice. Hirshfeld surface analysis also confirms asubstantial contribution of O⋅⋅⋅H/H⋅⋅⋅O interactions (23.3%) to the total Hirshfeld surface. H₆L exhibited enhanced fluorescence emission in response to Na⁺ with a detection limit of 40 × 10^− 8 M, facilitated by the inhibition of the C = N based isomerisation and inhibition of the excited-state intramolecular proton transfer mechanism. The sensing capability of H₆L towards Na⁺ ions was confirmed by electronic and IR spectra, theoretical studies, Job’s plot and Benesi-Hildebrand method, collectively demonstrating ground-state complex formation and a 1:2 binding stoichiometry between H₆L and Na⁺ ions. The sensor’s practical application for detecting Na⁺ ions was demonstrated by creating sensor-coated paper strips. Additionally, the compound was evaluated for its in vitro anticancer activity against MCF7 breast cancer and A549 lung adenocarcinoma cell lines. The IC₅₀ values indicate excellent cytotoxic activity against MCF7 cells (40.37&#xa0;µg/mL) compared to A549 cells (82.30&#xa0;µg/mL). To further explore the mechanisms underlying its anticancer activity, molecular docking studies were performed against enzyme targets 4IGK and 2ITO, which validate the in vitro findings.</p>