Design and development of a Schiff base–based sensor aiding different spectroscopic techniques for metal ion detection via optical and Raman methods

• Schiff base ligand (L) investigated as a multi-spectroscopic metal-ion sensor using UV–Visible, fluorescence, and Raman techniques. • UV–Visible studies reveal strong selectivity toward Fe³⁺, with the appearance of a new LMCT band at 450–500 nm and a distinct colour change from yellow to red enabling naked-eye detection. • Fluorescence spectroscopy shows a selective turn-on response toward Ni²⁺, including a significant blue shift from 500 nm to 466 nm, allowing detection at low concentrations. • Raman-active thin film of L selectively detects Cu²⁺ and Fe³⁺, verified by characteristic low-frequency Cu–N, Cu–O, Fe–Cl, and Fe–N/O vibrational bands. • Combined UV–Vis, fluorescence, and Raman results establish ligand L as a versatile platform for solution-phase and solid-state metal-ion sensing applications. Schiff base ligands are widely recognized for their exceptional metal-coordination abilities, structural tunability, and strong optical responsiveness, making them valuable platforms for chemical sensing technologies. In this study, we investigate the metal-ion sensing behaviour of the Schiff base ligand, 3-((2-(-(1-(2-hydroxyphenyl)ethylidene)amino)ethyl)imino)-2-pentone, using a combination of UV–visible absorption, fluorescence, and Raman spectroscopic techniques. The ligand exhibits prominent and selective responses toward different transition metal ions: a distinct naked-eye colour change and optical selectivity for Fe³⁺ in solution, significant fluorescence enhancement upon interaction with Ni²⁺, and characteristic Raman spectral signatures for Cu²⁺ and Fe³⁺ when incorporated into a thin film. A solid-state Raman sensor was further developed by immobilizing the ligand as a thin film enabling selective and stable metal–ligand interactions under ambient conditions. These findings underscore the versatility of Schiff base ligands and their strong potential for designing multifunctional solution-phase and solid-state sensors for transition metal ions.