A novel fluorescent chemosensor enables dual-channel selective “turn-on” detection of Hg2+ and Ag+via distinct thiophilic effects, essential mechanisms, and excellent sensing performance for mercury(ii) in aggregated states

Abstract

The presence of Ag⁺ or Hg²⁺ usually interferes with the detection of another ion due to their similar reaction activity. In this work, a smart fluorescent probe DTPAS containing two thioketal groups was elaborately designed, which realized dual-channel selective “turn-on” detection of Hg²⁺ (red fluorescence) and Ag⁺ (green fluorescence) with LODs of 0.092 μM and 0.86 μM, respectively. The different signals for Hg²⁺ and Ag⁺ ions occur due to the distinct thiophilic effect, wherein the former converts both thioketal of DTPAS to carbonyl groups immediately (product DTPAO) whereas the latter can only convert one of them (product DTPAOS). The mechanism of the chemosensor was fully verified using ¹H NMR, FTIR and MS spectra. Additionally, Hg²⁺-triggered ACQ (DTPAS) to AIE (DTPAO) transformation endows the probe with excellent turn-on sensing performance for Hg²⁺ in the aggregated and solid-states. The PL intensity of the probe in aggregates (f_w = 98%) exhibited a dramatic enhancement (486-fold) with fluorescence changing from dark to brilliant yellow after encountering Hg²⁺. Similarly, in the solid state, the fabricated test strip could signify Hg²⁺ in water with an LOD of 1 × 10⁻⁶ M. Other common metal cations did not interfere with the detection process, and the probe could rapidly detect Ag⁺ and Hg²⁺ ions in real water samples quantitatively. Meanwhile, crystal analysis and theoretical calculations were conducted to explore the origin of their opposite ACQ and AIE activities.