LUMINESCENCE AND CHARGE-TRANSFER .3. THE USE OF CHROMOPHORES WITH ICT (INTERNAL CHARGE-TRANSFER) EXCITED-STATES IN THE CONSTRUCTION OF FLUORESCENT PET (PHOTOINDUCED ELECTRON-TRANSFER) PH SENSORS AND RELATED ABSORPTION PH SENSORS WITH AMINOALKYL SIDE-CHAINS

7-Methoxycoumarin, 3-aminobenzimidazo[2,1 -a]benz[de]isoquinolin-7-one and 4-nitroaniline derivatives, useful as chromatographic derivatizing agents, dyes and solvent polarity indicators respectively, are easily transformed into optical pH sensors 3a-c, 4a-c and 5a-c respectively by attachment of a proximal, non-adjacent amine moiety. The availability of ICT (internal charge transfer) excited singlet states in each of these sensor families leads to protonation-induced wavelength shifts of their electronic absorption spectra. A similar phenomenon is observed in those fluorescence emission spectra where the proton-free form of the sensor is weakly emissive due to the sluggishness of the designed PET (photoinduced electron transfer) process. Except for these differences, sensors 3a-c and 4a-c show the expected pH dependence of fluorescence quantum yields, thus extending the scope of the fluorescent PET pH sensor design logic to electronic push-pull fluorophores besides aromatic hydrocarbons.