A new tridentate sulfur receptor as a highly sensitive and selective fluorescent sensor for Cu2+ ions

The introduction of Lawesson's reagent into a bis-rhodamine spirolactam system afforded a new fluorescent sensor for Cu(2+) ions, SRR, which contained a new tridentate sulfur ligand. SRR showed excellent specificity for Cu(2+) ions over other cations (including Cu(+), Hg(2+), and Fe(3+)), very high sensitivity (10 nM), and a rapid response time (3 min). The detection mechanism was investigated by (1)H NMR, (13)C NMR, (31)P NMR, and ESR spectroscopy, MS, and Gaussian calculations. Coordination of a Cu(2+) ion to the tridentate sulfur ligand, which promotes ring-opening of the rhodamine groups, followed by a spontaneous reduction reaction (Cu(2+) into Cu(+)), has been proposed as the sensing mechanism.