A coumarin-derived Cu-fluorescent chemosensor and its direct application in aqueous media.

A novel coumarin-based receptor bearing a benzohydrazide (FCBH) was developed as a fluorescent chemosensor with high selectivity toward Cu. The sensor was successfully applied to the monitoring of Cu in aqueous solution. After the addition of Cu to FCBH, the color of the solution changed from greenish-yellow to red, and the absorption band at 457nm red-shifted to 517nm. The fluorescent green color of FCBH disappeared and the fluorescence emission was completely quenched in the presence of Cu. Upon the addition of Cu, deprotonation of FCBH occurred, and a 1:1 metal-ligand complex formed. DFT theoretical investigation was carried out to understand the behavior of the sensing probe toward Cu. Additionally, the quenched fluorescence of the FCBH-Cu complex was restored upon the addition of CN ions. The possible sensing mechanism of FCBH toward Cu was derived from experimental and theoretical examinations.