1,8-Naphthyridine-based fluorescent receptors for picric acid detection in aqueous media

We utilized the potential applications of 1,8-naphthyridine-based sensors for the detection of various nitroaromatics such as picric acid (PA), 3-nitrophenol (NP), 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB), 4-nitrotoluene (NT), nitrobenzene (NB) and nitromethane (NM). Among the various nitroaromatic analogues, nap-OH (1) and nap-Cl (2) sense picric acid (PA) much more efficiently and with very low detection limits (1.12 and 0.96 ppm, respectively), owing to favourable electron and/or energy transfer mechanisms along with potential electrostatic interactions. Interestingly, both sensors 1 and 2 detect PA in aqueous media (H2O/CH3OH, 8 : 2) with the same quenching efficiency as in neat CH3OH, resulting in cheap, sensitive and environmentally friendly detection methodology. Therefore, use of these molecules for picric acid detection in aqueous and methanolic solutions, having low detection limits along with exceptional quenching constants (kSV) meets the present need. In addition, sensors 1 and 2 exhibit instant visualization of trace amounts of PA in both the solid-state and when using test strips.