A selective sensor 1 for the fluorescent imaging of Cd2+ in living cells has been designed and synthesized based on an internal charge transfer (ICT) mechanism. It can distinguish Cd2+ from Zn2+ and can be used in both general fluorescence intensity microscopy and ratiometric fluorescence microscopy.

Phenyl-1H-anthra[1,2-d]imidazole-6,11-dione (1) and its derivatives (2 and 3) have been investigated as new colorimetric and ratiometric fluorescent chemosensors for fluoride. Acute spectral responses of 1 and 3 to fluoride in acetonitrile have been observed: an approximately 100 nm red shift in absorption and fluorescence emission and a very large ratiometric fluorescent response (R max /R min is 88 for sensor 1 and 548 for sensor 3). From the changes in the absorption, fluorescence, and 1 H NMR titration spectra, proton-transfer mechanisms have been deduced. In ground states, a twostep process has been observed: first, the formation of the sensor-fluoride hydrogen-bond complex [LH‚‚‚F] -and then the fluoride-induced deprotonation of the complex to form L -and FHF -. In excited states, the excited-state intermolecular proton-transfer made a contribution to the deprotonation. The selectivity for F -can be tuned by electron push-pull properties of the substituents on the phenyl para position of the sensors. Sensor 1 shows the best selectivity. The excellent selectivity of 1 for F -is attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F -, CH 3 CO 2 -, and H 2 PO 4 -to proton.