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.
The fluorescence spectra in cyclohexane of a series of benzanilides(BAs) with different \%para\% substituents at the anilino moiety revealed that BAs emitted dual fluorescence, with one normal weak emission at ca . 330 nm and an abnormally long wavelength emission ranging from 460 to 550 nm. The long wavelength emission was found strongly dependent of the electron donating capacity of the substituent at the anilino moiety and a stronger electron donating substituent led to a red shift in the emission. The energies of the long wavelength emission of the BAs were correlated to the oxidation potentials of the donors, E \-\{D/D +\}, and a nice linear correlation was found with a slope of +0 66, which clearly pointed to the charge transfer character of the emissive state for the long wavelength emission and the high decoupling extent of the charges in the CT state. This is the first report that shows the direct evidence for the CT nature. The results might be of significance in understanding the photophysics of peptide and protein and in designing novel fluorescent chemosensors.
