THE PHOTOPROTOLYTIC REACTIONS IN THE SYSTEMS IMMOBILIZED ON SILICA WITH A CATIONIC POLYELECTROLYTE
The protolytic and photoprotolytic reactions were studied for the model systems of 2-naphthol and for sulfonated 2-naphthols in the immobilized state. It was found that the fi xation of indicators with a cationic polyelectrolyte leads to the shift of pKa of the ground state to a more acidic value. The value of this shift depends on the number of sulfo-groups in the molecule and reaches 1.2 units for the disodium salt of 2-naphthol-3,6,8-trisulfonic acid. However, the photoprotolytic reaction in the lower singlet-excited state proceeds in the same way as for an unimmobilized substance, and no signifi cant shift in pKa* is observed. The possibility of a fl ow-through acidity sensor using the ratio of the intensities of the fl uorescence bands of the protonated and deprotonated forms of the indicator is shown.