Fluorometric detection of nitroaromatics by fluorescent lead complexes: A spectroscopic assessment of detection mechanism

Three Schiff base ligands such as 2‑[(2‑Hydroxy‑3‑methoxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL1), 2‑[(2‑Hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL2), 2‑[(3,5‑Dichloro‑2‑hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL3) have been synthesized by condensation of aldehydes (such as 3,5‑Dichloro‑2‑hydroxy benzaldehyde, 2‑Hydroxy‑benzaldehyde, and 2‑Hydroxy‑3‑methoxy‑benzaldehyde) with Tris‑(hydroxymethyl)amino methane and characterized by IR, UV–vis and ¹H NMR spectroscopy. Then all these three ligands have been used to prepare Pb(II) complexes by reaction with lead(II) acetate tri-hydrate in methanol. In view of analytical and spectral (IR, UV–vis and Mass) studies, it has been concluded that, except HL2, other two ligands form 1:1 metal complexes (1 and 3) with lead. Between two complexes, complex 3 is highly fluorescent and this property has been used to identify the pollutant nitroaromatics. Finally, the quenching mechanism has been established by means of spectroscopic investigation.