Acenaphtoquinoxaline as a selective fluorescent sensor for Hg (II) detection: experimental and theoretical studies

A new fluorescent chemosensor based on quinoxaline was successfully synthesized through a facile and green catalytic reaction of ortho-phenylenediamine (O-PDA) and acenaphthylene-1,2-dione in the presence of SBA-Pr-SO₃H. Prepared a "switch-off" quinoxaline-based receptor to recognized Hg²⁺ ion in high selectively and, without any interference from other metal ions, was developed. The photophysical behavior of this fluorophore was studied in acetonitrile by using fluorescence spectra. The fluorescence properties of several cations to acenaphtoquinoxaline were investigated in acetonitrile, and the competition test displayed that the probe fluorescence changes were specific for Hg²⁺ ion. The obtained results have shown high selectivity and sensitivity only for Hg²⁺. Also, the detection limit was as low as 42 ppb, and a top linear trend was observed between the concentration of Hg²⁺ ions and fluorescence intensity. The binding stoichiometry between chemosensor L and Hg²⁺ was found to be 1:1. Moreover, a computational study was performed to obtain an electronic description of the fluorescence emission and quenching mechanisms. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.