Lactam functionalized Anthraquinone: A Versatile Recognition scaffold for detection of S^2- ions.

We have desigined and synthesised anthraquinone based sensor equipped with a lactam unit for selective and sensitive recognition of sulphide ions (S^2-/HS^-) in organic media via a Bronsted acid base interaction. The presence of a proton donor unit (NH) functioning as Bronsted acid and electron acceptor unit (C=O) is proven to have strong interaction with sulphide ions which act as a Bronsted base in this system. The sensing behaviour was typically evaluated with both colorimetric and flurometric analysis . Upon addition of sulphide ion, the probe displayed a significant colour change which attributed to the deprotonation of acidic H of lactam NH unit, accompanying significant changes in ICT pathway. Job’s plot indicated equimolar (1:1) complex formation between anion and the probe and the binding constant was found to be 2.1 × 10⁶ M⁻¹. The lactam based probe exhibited detection limit of 0.3 µM, which is way below the permissible limit for sulphide ions in drinking water (2.1 µM) set by the World Health Organization, suggesting that the developed sensor is suitable for on-site detection of sulphide ions. The synthesised receptor was grafted on Whatman paper strips for mobile and real-time detection of sulphide ions. The proposed study presents a promising tool for selective detection of sulphide ions.