Novel Coumarin-Substituted Cyclophosphazene as a Fluorescent Probe for Highly Selective Detection of 2,4,6-Trinitrophenol

Nitroaromatic compounds (NACs) such as 2,4,6-trinitrophenol (TNP), commonly known as picric acid (PA), hold widespread application in industries such as dyestuff production, wood preservation, explosives manufacturing, insect control, and photographic development. In this study, the organic-inorganic hybrid 4,4',4″,4‴,4″″,4‴″-((1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine-2,2,4,4,6,6-hexayl)hexakis(oxy))hexakis(2<i>H</i>-chromen-2-one) (<b>Cpz-4-HC</b>) was synthesized via the nucleophilic substitution reaction of 4-hydroxycoumarin (4-HC) with hexachlorocyclotriphosphazene (HCCP). The structure of Cpz-4-HC was fully characterized by Fourier transform infrared (FT-IR), ¹H-, ¹³C-, and ³¹P NMR, and HRMS. <b>Cpz-4-HC</b> is used as a chemical fluorescence sensor for the detection of TNP, with a <i>K</i> _SV value of 4.71 × 10⁴ M^-1 and a low limit of detection (LOD) of 0.334 ppm over some other analytes such as 2,4-DNP, 4-NP, 2-NP, 1,3-DNB, 2,4-DNT, and 2,6-DNT in water. The sensing mechanism was elucidated through spectral overlap analysis, indicating the resonance energy transfer as the dominant quenching process. Dynamic quenching was established through fluorescence lifetime studies, further affirming <b>Cpz-4-HC</b> capability for environmental monitoring. Experimental and theoretical analyses underscored TNP's strong interaction with <b>Cpz-4-HC</b>, corroborating its suitability for sensing applications. Their recyclable nature and ultrafast response time make them highly suitable for detecting TNP, even in the presence of other interfering nitroaromatics. This study provides novel perspectives on the development and formulation of a chemical fluorescent sensor for TNP, utilizing a straightforward synthesis method.