A reversible colorimetric probe for carbonate ion detection with applications in environmental monitoring and molecular logic

A highly conjugated donor-acceptor molecular receptor, 2-amino-3-((2,4-dinitrobenzylidene)amino)maleonitrile (R), has been designed and synthesized for the selective colorimetric recognition of carbonate ions in environmental samples. The receptor exhibited an immediate and distinct optical response toward carbonate anions, accompanied by a remarkable bathochromic shift of 172 nm in the charge-transfer absorption band, enabling rapid naked-eye detection. The sensing process showed excellent selectivity over competing anions and operated efficiently under environmentally relevant conditions. Importantly, the recognition event was reversible in the presence of calcium ions, allowing regeneration and repeated use of the receptor system without significant loss of performance. To enhance practical applicability, the sensing platform was successfully translated from solution-phase detection to portable solid-state test strips capable of on-site carbonate monitoring. The combination of high sensitivity, visual detectability, reversibility, and operational simplicity highlights the potential of receptor R as an economical analytical tool for alkalinity sensing in water and soil samples. Furthermore, the reversible switching behaviour of the receptor-anion ensemble was exploited to construct molecular-level Boolean arithmetic functions and memory operations, demonstrating its utility in supramolecular logic applications.