A Rare Natural Benzo[k,l]xanthene as a Turn-Off Fluorescent Sensor for Cu(2+) Ion

Rapid and efficient analyses of copper ions are crucial to providing key information for Cu(2+) in living cells because of their biological importance. In this study, we reported one new turn-off fluorescent sensor for Cu(2+) with a benzo[k,l]xanthene core, which served as an efficient cation sensor for copper ion over a wide range of other cations (Na(+), K(+), Ag(+), Hg(2+), Cd(2+), Co(2+), Ni(2+), Zn(2+), Mg(2+), and Fe(3+)) owing to the catechol group in the aromatic core. The sensor showed selectivity for Cu(2+) over other ions; the logK(β) for Cu(2+) binding to compound 1 had a value of 13.265. In the presence of Cu(2+), sensor 1 provided significant fluorescence decrement; Co(2+), and Ni(2+) caused a fluorescence decrement when employed at a higher concentration than Cu(2+), while Na(+), K(+), Hg(2+), Cd(2+), Zn(2+), and Mg(2+) metal ions produced only minor changes in fluorescence intensity. Fluorescence experiments demonstrate that compound 1 may have an application as a fluorescent probe for detecting Cu(2+) with a limit of detection of 0.574 µM.