Cascade sensitive and selective fluorescence OFF–ON–OFF sensor for Cr3+ cation and F− anion

Cascade recognition of trivalent chromium cation (Cr 3+ ) and fluoride anion (F − ) via rhodamine-urea methacrylate-based fluorescent probe (RhBUA) and its subsequent cationic complex was reported. The non-fluorescent rhodamine derivatives can selectively detect Cr 3+ cation over some other metal ions in CH 3 CN–H 2 O (90/10, v/v, pH 7.0) solutions with a 1:1 stoichiometry, leading to prominent fluorescence OFF–ON switching. The obtained RhBUA–Cr 3+ complex can subsequently serve as a sensitive and selective chemosensor for F − ion. Complete signal quenching (fluorescence ON–OFF switching) can also be observed, ascribing to the extraction of Cr 3+ cation and the resulting deformation of RhBUA–Cr 3+ complex.