A novel N-(5-(1H-benzo[d]imidazole-2-yl)-4-(2-hydroxybenzylideneamino)pyrimidin-2-yl)-4-methylbenzenesulfonamide (SBSB) Schiff-base as colorimetric sensor for selective Pb(II) detection: Experimental and DFT insight

Lead (Pb(II)) pollution poses severe risks to environmental and human health due to its toxicity, persistence, and bioaccumulation in ecosystems. In response to the pressing need for simple, cost-effective, and selective detection of Pb(II), this study reports the design and synthesis of a novel colorimetric Schiff-base chemosensor, N-(5-(1H-benzo[d]imidazole-2-yl)-4-(2-hydroxybenzylideneamino)pyrimidin-2-yl)-4-methylbenzenesulfonamide (SBSB). The sensor demonstrates high selectivity and sensitivity for Pb(II) ions over a wide range of competing mono-, di-, and trivalent metal ions and common anions in aqueous solution. Upon binding with Pb(II), SBSB forms a stable 1:1 complex, producing a distinct pale orange color visible to the naked eye. The detection mechanism is supported by UV–Vis spectroscopy, showing a red-shift from 305 nm (π–π∗) to 425 nm (MLCT). The sensor exhibits optimal performance at pH 7 and 35 °C with a response time of 30 min. The limit of detection (LOD) was determined to be 6.61 μM, and the binding constant was calculated as 2.65 × 10⁴ M⁻¹, reflecting strong affinity and complex stability. Notably, SBSB retained its performance in real water samples, achieving recovery rates between 98 and 102 %, confirming its potential for practical applications in environmental monitoring. Computational studies, including DFT and NBO analyses, further confirmed the sensor's high binding efficiency and reduced HOMO-LUMO energy gap (from 3.75 eV in free SBSB to 2.47 eV in the Pb-SBSB complex), validating the observed charge-transfer transitions. This work introduces SBSB as a novel, robust, and field-deployable chemosensor for Pb(II) detection, offering an attractive alternative to conventional analytical techniques by combining visual detection, environmental compatibility, and high analytical performance.