Chromone derived effective probe for the detection of metal ion (Cu2+) and chemical explosive (p-nitrotoluene)

Abstract

A new chromone based Schiff base probe 1,3-bis({[(4-oxo-4H-chromen-3-yl)methylidene]amino})urea (CCH) has been synthesized in one step by the condensation reaction between 3-formylchromone and carbohydrazide in a 2:1 M ratio. The characterization of CCH was done by employing various analytical techniques; FTIR, 1H NMR, 13C NMR, HRMS and FESEM. The probe CCH showed a naked eye colorimetric response from colourless to yellow for the Cu2+ ions with greater selectivity over other metal ions taken for analysis. The binding constant and limit of detection of CCH for Cu2+ ions were calculated to be 4.5 × 105M−1 and 11.4 × 10−7M, respectively, using UV–Visible titrations. The DFT (Density functional theory) results also confirmed the experimental studies. In addition, CCH has shown its applicability for the detection of nitroaromatic compound i.e., p-nitrotoluene (pNT). The sensing mechanism of pNT was studied by UV–Visible and fluorescence studies. A significant quenching of the emission intensity of CCH at 402 nm in the case of pNT was noted above other nitroaromatics taken for study. The binding constant and limit of detection for pNT were calculated to be 1.2 × 105 M−1 and 25 × 10−9M, respectively, using B-H plot. The presence of other nitroaromatics negligibly affects the detection of pNT in CCH solution, as confirmed by anti-interfering studies. FESEM analysis of CCH with pNT confirmed the formation of an adduct. The time resolved fluorescence lifetime measurement also ensured the CCH-pNT adduct formation and the average life time data revealed that the quenching process was dynamic. The CCH-pNT adduct formation was also validated via DFT studies. Overall results suggested that the Schiff base CCH could be an efficient option to detect Cu2+ ions colorimetrically and pNT by fluorimetrically.