Intramolecular charge transfer(ICT) dual fluorescence of p-dimethylamino-benzoylhydrazine(DMABH) in acetonitrile was found to show a highly selective response to HSO - 4 over several other anions. The intensity ratio of the CT to LE emission and the total fluorescence intensity of DMABH decreased with increasing bisulfate concentration. While the dual fluorescence response was very similar to that of DMABA at a low HSO - 4 concentration, the CT intensity decreased drastically and the LE intensity remained almost constant, however, the difference was observed at a high HSO - 4 concentration, in which both the CT and LE intensities of DMABH decreased. A different recognition mechanism from that of DMABA was suggested for DMABH in which hydrogen bonding and protonization were the recognition interactions at low and high HSO - 4 concentrations, respectively.
