Active Hydrogen Free, Z-isomer selective, isatin derived “Turn on” fluorescent dual anions sensor

Abstract An efficient 1-(prop-2-yn-1-yl)-3-(quinolin-3-ylimino)indolin-2-one (PQI) fluorescence "on-off" sensor for anions has been designed to detect dual F⁻and NO₃⁻ ions anions in an aqueous medium without interference. Superior UV light sensing activity against F⁻ and NO₃⁻ions is exhibited by the Z-isomer of the isatin-based π-conjugated quinoline isomer, which is free of Lewis acid and active hydrogen sites. The act of turning on the fluorescence is accomplished using the PET "on-off" mechanism. The non-covalent interactions that mediate the interaction between the probe molecule and anions are thought to be the low electron density covalently bonded isatin N-methylene moiety (-N-CH₂-) of the propargyl group of the probe molecule for F- ions and the terminal acidic proton of propargyl for NO₃⁻ ions, respectively. The forms of anion binding with PQI are explained by conceivable mechanisms as shown by ¹H and ¹³C NMR titrations. The selectivity of anions sensing may be affected by the bucked structure of the Z-isomer. The computed association constant values for PQI and F⁻ and NO₃⁻ ions are 2.5 × 10⁴ M⁻¹ and 2.2 × 103 M⁻¹, respectively, indicating strong interaction between PQI and anions. The relationship between anions and probes is investigated using a jobs plot analysis, and the findings indicate that F⁻and NO₃⁻ ions are in a 1:1 complexation with PQI.The calculation indicates that the probe's limit of detection (LOD) for F⁻ and NO₃⁻ ions is 6.91 × 10⁻⁷ M⁻¹ and 9.93 × 10⁻⁷ M⁻¹, respectively. The low limit of detection (LOD) of the suggested PQI fluorophore is within the WHO-recommended limit for both F⁻ and NO₃⁻ ions.