Porphyrin And Triphenylimidazole-based Fluorescent Probes For Hg²⁺

Mercury(Hg) is a toxic heavy metal, and even low concentration of that has harmful effects on human health. As a global pollutant, Hg has received considerable attention due to its toxic, persistent, and bioaccumulative natures. Hg can be absorbed through the skin and mucous membranes. Hg can be converted to methylmercury(Me-Hg) and accumulated in the food chain, posing a potential threat to humans’ health. Even a trace amount of Hg intake can lead to acute or chronic damage to the human body, in which toxic effects include damage to the brain, kidney, and lung. Therefore, determination of Hg at ultra trace level is very important. Among various detection methods for mercury ion(Hg2+) species, fluorescent probes have received much attention owing to their sensitive and easy-to-operate features.In this paper,we have designed and synthesized two fluorescent probes for Hg2+, and studied the Hg2+ sensing performance using UV-vis absorption and fluorescence spectra. The specific contents are as follows:(1) We demonstrated a porphyrin-thymine based chemosensor(4T-ZnP) for Hg2+ determination. This chemosensor was synthesized by direct condensation of thymin-1-ylacetic acid with zinc tetraaminoporphyrin, which has a porphyrin core as the fluorophore and four thymine(T) moieties as the specific interaction sites for Hg2+. The probe(4T-ZnP) exhibited split Soret bands with a strong band at 429 nm in a DMF/H2O(7/3, v/v) mixed solvent as well as a strong emission band at 614 nm. Upon the addition of Hg2+, the probe displayed strong fluorescence quenching due to the formation of T-Hg2+-T complexes. With the aid of the fluorescence spectrometer, the chemosensor in the DMF/H2O(7/3, v/v) mixed solvent(0.3 μM) exhibited a detection limit of 6.7 nM, interferences from other common cations. The probes displays advantages such as highly sensitivity, selectivity and reversibility.(2) We demonstrated a triphenylimidazole based “turn on” probe(TPI-S) with simple structure for Hg2+ determination. Addition of Hg2+ cause a 45 nm red shift in the wavelength of the maximum absorbance from 318 to 363 nm. The probe exhibited a fluorescent color change from colorless to bright yellow upon addition of Hg2+, allowing for detection with the naked eye. TPI-S displayed high sensitivity and selectivity towards Hg2+ over other metal ions with detectable fluorescent signals. The probe in the DMF/H2O(7/3, v/v) mixed solvent(2.0 μM) exhibited a detection limit of 4.3 nM. This mechanism was confirmed by the UV-vis spectra, Job’s experiment, MALDI-TOF mass spectrum, infrared spectrum and 1H NMR spectrum.