Inner Filter Effect Based Selective Detection of Nitroexplosive-Picric Acid in Aqueous Solution and Solid Support Using Conjugated Polymer

A new polyfluorene derivative, poly[4,4'-(((2-phenyl-9H-fluorene-9,9-diyl)bis(hexane-6,1-diyl))bis(oxy))-dianiline)] (PFAM) was synthesized via the Suzuki coupling polymerization method in high yields for the rapid and specific recognition of nitroexplosive picric acid (PA) at 22.9 picogram level on solid support using paper strips and at 13.2 ppb level in aqueous solution. The polymer PFAM was well-characterized by means of NMR, UV-vis, fluorescence, time-resolved photoluminescence (TRPL) spectroscopy and cyclic voltammetry. The amplified signal response exclusively for PA was achieved via a strong inner filter effect (IFE), a phenomenon different from the widely reported ground-state charge transfer and/or Forster resonance energy transfer (FRET) based probes for nitroaromatics detection. Pendant amine groups attached on the side chains of PFAM provide enhanced sensitivity and exceptional selectivity via protonation assisted photoinduced electron transfer (PET) even in the presence of most common interfering nitroexplosives, as well as other analytes usually found in natural water. Thus, the PFAM based platform was demonstrated for monitoring traces of PA at very low levels even in competitive environment in solution as well as solid state.