Dual-channel fluorescence “turn on” probe for Cu2+

Two naphthalimide-based turn-on chemosensors were designed and synthesized. These sensors exhibited high sensitivity and selectivity for Cu2+ over other cations. In addition, two different emission channels emerged in a diaminomaleonitrile derivative when the sensor was exposed to different concentration of copper cation in acetonitrile solution. The recognition process in the first channel involves the blocking of the photo-induced electron transfer when imine and amine groups coordinated to the first copper ion, whereas electron-withdrawing ability of the imine group might be enhanced via nitrile group binding with the second copper ion. This gave a cautionary change in fluorescence emission in both intensity and color in response to the concentration change of Cu2+.