A highly selective ratiometric and colorimetric detection of Ni2+ and Cu2+ ions using Schiff base ligand

•Synthesis of chemosensor 4‑bromo-2-((Z)−1-(((Z)−2-hydroxybenzylidene)-hydrazineylidene)ethyl)phenol (BHEP).•BHEP acted as a UV–visible, fluorescence, and colorimetric to detect Ni2+and Cu2+ions.•Association stoichiometry and affinity, limits of detection, quantification, and linear ranges were determined.•The colorimetric observations checked BHEP reversibility with Cu2+and non-reversibility nature with Ni2+ ions.