Two naphthalimide based chemosensors were synthesized. Upon the addition of OH- or F-, the solution color turned from pink to blue due to the proton elimination of N-H/O-H. The electron density increased on the nitrogen atom and enhanced the intramolecular charge transfer, which resulted in a red-shift of the absorption band. This color change was reversible with H+/MeOH addition and can be detected with the naked eye. The selectivity of the two dyes toward OH-/F- compared with other anions was investigated. The underlying signal mechanism was interpreted by the HOMO/LUMO potentials. Significantly lowered energy gap supported the red-shift absorption band.