A novel sensing capabilities and structural modification from thiourea to urea derivative by Hg(ClO4)2: Selective dual chemodosimeter for Hg2+ and F− ions

Abstract

A new rhodamine-6G phenylthiourea derivative (L1) condensed product was developed as a fluorescent and colorimetric dual chemosensor in acetonitrile with more selective towards Hg2+ and F− ions. Hg2+-promoted spirolactam ring opening of the rhodamine moiety induced urea formation through the diphenylcarbodiimide intermediate from the thiourea moiety. It demonstrates high selectivity for sensing Hg2+ with about 700-fold enhancement in fluorescence emission intensity and micromolar sensitivity (limit of detection 4.52×10−7M) in comparison with other various metal ions. Hg2+ ions coordinated reversibly to L1, forming a 1:2 metal–ligand complex. The thiourea moiety provided an anion binding site, and the rhodamine system was responsible for fluorescence. In turn, the chemosensor L1 acted as a selective chemosensor toward F− among various anions. Thus, L1 associated with F− with 1:1 stoichiometry. A recognition mechanism based on the binding modes of Hg2+ and F− ions were proved by the analytical techniques like UV–vis, changes in fluorescence, 1H NMR, FT-IR, ESI-mass and HRMS. In addition, this chemosensor exhibited highly selective and sensitive recognition of azide (N3−) anions upon the addition of Hg2+ with a color change back to colorless in the same solution.