The synthesis and characterization of a highly fluorescent core-substituted naphthalene diimide sensor (phi = 0.34) bearing a bis-sulfonamide group is described. The compound shows a unique selectivity and reactivity for the fluoride ion over other anions in CHCl3 by a two-stage deprotonation process leading to a colorimetric response. In DMSO solution, the sensor is shown to be highly selective for fluoride (K-a similar to 10(6) M-1) over other anions with more pronounced changes In absorption characteristics.