A colorimetric and “turn-on” fluorescent chemosensor for Zn(II) based on coumarin Shiff-base derivative

A coumarin Shiff-base derivative, 7-hydroxy-3-(2-hydroxybenzylideneamino)-2H-chromen-2-one (CSB), was obtained by simple two-step organic synthesis from cheap and commercially available starting materials. CSB has nearly no fluorescence in CH3CN solution. However, in the presence of Zn(II) ion, a “turn-on” fluorescence was observed. Other metal ions in CSB solution show very little emission or do not show any emission. CSB can also be used as a colorimetric chemosensor for Zn(II), which is easily observed from colorless to yellow by the naked eye. The absorption maximum of CSB shows a large red shift from 374 to 452 nm upon addition of Zn(II).