Development of 2-hydroxy-naphthaldehyde functionalized Schiff base chemosensor for spectroscopic and colorimetric detection of Cu2+ and Pd2+ ions

• Synthesis of 4-((Z)-1-(((Z)-(2-hydroxynaphthalen-1-yl)methylene)hydrazineylidene)ethyl)benzene-1,3-diol ( HMHEB ). • HMHEB acted as a UV–visible, fluorescence, colorimetric, and electrochemical sensor to detect Cu 2+ and Pd 2+ ions through Photoinduced electron transfer (PET), charge transfer, and d-d transition. • Association affinity, limits of detection, quantification, and linear ranges were determined. • The colorimetric observations checked HMHEB reversibility with Cu 2+ and Pd 2+ ions. The colorimetric detection of metal ions is significantly applied for industrial, ecological, and medical applications. Here, we synthesize 4-((Z)-1-(((Z)-(2-hydroxynaphthalen-1-yl)methylene)-hydrazineylidene)ethyl)benzene-1,3-diol a new chemosensor that acts for sensitive and selective detection of Cu 2+ and Pd 2+ ions to the ligand. The recognition is determined by redshift in UV–visible, emission intensity changes in fluorescence, colorless to yellow coloration, and cyclic voltammetric signal changes with the addition of Cu 2+ and Pd 2+ ions to the ligand. The insights into the color changes are described visually and under different wavelengths of light. The designed colorimetric sensing model is developed as paper, cotton, and mask-based assay for Pd 2+ and Cu 2+ ion. The chemosensor reversibility is checked with the addition of ethylenediaminetetraacetic acid (EDTA), and color changes are observed with naked eyes. The infrared (IR) spectral analysis describes ligand's binding behavior towards selective metal ions. In addition, the chemosensor works for low detection limit (4.906 × 10 -7 M for Cu 2+ , 9.802 × 10 -7 M for Pd 2+ ), limit of quantitation (1.636 × 10 -6 M for Cu 2+ , 3.267 × 10 -6 M for Pd 2+ ) with good association affinity (1.273 × 10 5 M −1 for HMHEB -Cu 2+ binding, 6.983 × 10 10 M −2 for HMHEB -Pd 2+ binding).