Naphthalene-glycine conjugate: An extremely selective colorimetric chemosensor for iodide ion in aqueous solution

Abstract A distinctive water soluble chemosensor based on naphthalene-glycine conjugate has been designed. The synthesized molecule is highly selective and sensitive towards detection of iodide ion in aqueous solution. The probe exhibits a color change from colorless to pale pink that can be detected by naked eye which is a simple and cost effective detection method. Further, addition of iodide ion led to the complete diminution of the fluorescence intensity of ligand 1 . Under optimal conditions, its response was linearly proportional to the concentration of I − ion (range from 6.25 × 10 −6 to 3.12 × 10 −5  mol L −1 ) with a detection limit of 30 nM. Based on the 1 H NMR titration, ESI–MS data and Job’s plot, the probable binding mode of this receptor with iodide ion has also been postulated and binding ratio of ligand to I − ion is found to be 2:1. This result is also supported by the theoretical calculation using DFT method. The molecular structure of 1 revealed the existence of different intermolecular C H/O and O H/N hydrogen bonds which led to the formation of a zig - zag linear 1D tape. Furthermore, the selectivity and sensitivity of the present probe towards iodide ion is also preserved on test kits made of cellulose bound filter paper and on supported solid silica.