Imidazole-based fluorescent probes: concomitant effects of N1 substitution and lone pair on selective recognition of picric acid

Abstract

A series of N1-functionalized imidazoles have been synthesized in very good yield. Due to their amphoteric nature, they selectively discriminate among different nitroaromatic compounds. The fluorescence spectra of all the luminophores are highly sensitive towards picric acid compared to other nitroaromatic compounds. The fluorescence method has a fast response, low cost, and high selectivity for picric acid over other nitroaromatic compounds. Electrochemical analysis was performed and verified using DFT calculations. The electrochemical properties were studied using cyclic voltammetry to calculate the HOMO–LUMO gap, and were also confirmed via theoretical study. The Stern–Volmer quenching constant and detection limit were found to be 6.68 × 10⁶ M⁻¹ and 446 ppb. The capability of luminophores to recognise picric acid was estimated using fluorescence, DFT analysis, and ¹H NMR spectroscopy. Thus, potential luminophores were synthesized as convenient and promising multifunctional sensors for toxic and explosive nitroaromatic analytes.