Efficient fluorescent chemosensors for HSO4(-) based on a strategy of anion-induced rotation-displaced H-aggregates. 
A novel fluorometric sensing strategy based on the anion-induced rotation-displaced H-aggregates of styrylindolium dyes was employed to enhance the selectivity of fluorescent chemosensors for HSO4(-) detection.  The marvelous anion-induced H-aggregate strategy opens new routes to simple synthesis of receptors for tetrahedral anionic species.