Ultrahigh sensitivity and extremely low limit of detection of picric acid with ionic-liquid modified poly(diphenylacetylene)

Abstract

Through the polymerization of a diphenylacetylene derivative and subsequent post-polymerization modification of the poly(diphenylacetylene), polymers with ionic liquid units of imidazolium as side chains and bromide anions (P2) and bis(trifluoromethylsulfonyl)imide (Tf₂N⁻) anions (P3) as counterions were obtained. P3 exhibited ultra-high sensitivity and an extremely low limit of detection (LOD) for picric acid (PA) detection in the solution state, the Stern–Volmer constant (K_sv) was 108 017 M⁻¹ and the LOD was 0.6 nM. Meanwhile, P3 exhibited good selectivity to PA over 8 other nitro-aromatics. Mechanistic studies confirmed the coexistence of static quenching and dynamic quenching mechanisms, and photo-induced electron transfer (PET) and resonance energy transfer (FRET) processes may also occur during quenching, with electrostatic interactions playing a crucial role. DFT calculation results confirmed that after the exchange of bromide ions with Tf₂N⁻ anions, the electron-accepting role of the ionic liquid units is significantly weakened, leading to significantly higher sensitivity of P3 compared to P2. And contact-mode detection of PA was conducted using readily available filter paper strips and spin-coating films to better simulate practical applications.