A novel cyanide-selective colorimetric and fluorescent chemosensor: First molecular security keypad lock based on phosphotungstic acid and CN− inputs

Highlights: • Our probe is commercially available with good photo stability and high quantum yield. • Both color and fluorescence change with long emission wavelength in aqueous media. • Characteristics of an ON–OFF–ON fluorescence switch. • The simple receptor for CN- detection with low detection limit (≪WHO). • Mimic the function of a security keypad lock on sequential addition of PTA and CN−. -- Abstract: Rhodamine B (RhB) an available dye has been developed as novel and efficient colorimetric and fluorometric chemosensor for cyanide ions in an absolutely aqueous media. The UV–vis absorption and fluorescent emission titrations experiments have been employed to study the sensing process. RhB could act as an efficient "ON–OFF" fluorescent response for phosphotungstic acid (H3PW12O40 or PTA) based on an ion associate process. Also (RhB+)3·PTA3− could operate as an "OFF–ON" fluorescent sensor for cyanide anions based on a ligand substitution process. It has been identified as highly sensitive probe for CN− which responds at 0.3 and 0.04 μmol L−1 concentration levels by absorption and fluorescent method respectively. Depending upon the sequence of addition of PTA and CN− ions into the solution, RhB could be as a molecular security keypad lock with PTA and CN− inputs. The ionic inputs to new fluorophore have been mimicked as a superimposed electronic molecular keypad lock. The results were compared successfully (>96%) with the data of a spectrophotometry approved method (EPA 9014-1) for cyanide ions