Rhodamine-based turn-on fluorescent and colorimetric chemosensor for selective Pb2+ detection: insights from crystal structure, molecular docking, real sample analysis, and logic gate applications

Lead (Pb²⁺) contamination remains a critical environmental and public health concern, necessitating its effective detection methods. In this study, we report the design and synthesis of a novel rhodamine-based Schiff base chemosensor (L), which demonstrates high selectivity and sensitivity for Pb²⁺ ions. The chemosensor exhibited distinct colorimetric and fluorescence responses, providing a practical and efficient approach for detecting Pb²⁺ in environmental and biological samples. Upon interaction with Pb²⁺ ions in acetonitrile, the sensor exhibited a distinct turn-on fluorescence response along with a noticeable colour change. The binding studies confirmed that sensor L bound to lead ions in a 1 : 1 ratio. This was determined using Job's plot and Benesi-Hildebrand (B-H) plot analyses, which also revealed a binding constant (K_a) of 0.954 × 10⁴ that indicated strong and specific interaction between L and Pb²⁺ ions. The limit of detection was found to be 3.77 nM for Pb²⁺ ions, demonstrating the remarkable sensitivity of the sensor. DFT calculations confirmed the stability of L-Pb²⁺ complex, where Pb²⁺ was coordinated to three atoms of L. Molecular docking analyses of L with human DNA (5VBN) indicated a binding affinity of -5.7 kcal mol^-1, highlighting its potential for DNA interactions and therapeutic use. The successful detection of Pb²⁺ in real water samples, solid-state sensing experiments, and filter paper-based assays demonstrated the practical applications of the sensor, highlighting its effectiveness in environmental monitoring.