The fluorescence response of 1 to different metal ions in ethanol was also investigated and shown in Figure S10a. The Cu2+ and Ni2+ ions quenched the emission but to different extents, whereas most of the other metal ions only slightly influenced the emission. Figure S10b shows the fluorescent response of the sensor 1 to increasing concentrations of Ni2+ ion. The sensor emission was significantly quenched by Ni2+ ion and the emission peak of sensor 1 at 430 nm was completely quenched upon addition of 5 equiv Ni2+ ion.