We have synthesized a copillar[5]arene-based fluorescence “on–off–on” sensor (DBP5) and used it for sequential fluorescence sensing for Fe³⁺ and F⁻ in H₂O/DMSO (1 : 9, v/v) solution. The copillar[5]arene DBP5 can produce blue fluorescence because it easily forms [c2]daisy-chain dimers by self-assembly behavior in solution. DBP5 exhibits high selectivity and sensitivity (1.65 × 10⁻⁸ M) to Fe³⁺. Moreover, the in situ formed DBP5–Fe³⁺ complex is further utilized to sense F⁻ through a complexation reaction with high selectivity and sensitivity (6.44 × 10⁻⁸ M) to F⁻. Furthermore, we designed the fluorescence switch of DBP5 between Fe³⁺ and F⁻. The structure of DBP5 was characterized by single crystal XRD.