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).

CSB, a coumarin Shiff-base derivative, could be used to detect Zn(II) by both fluorescence and the naked eye. CSB has nearly no fluorescence due to rapid isomerization in the excited state. However, this isomerization is stopped because of bonding to Zn(II) ion resulting in fluorescence “turn-on” with more than 1000-fold enhanced intensity.Figure optionsDownload as PowerPoint slide