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A. O. Naumova, A. S. Mugabutaeva, P. V. Melnikov, N. K. Zaitsev
The
photoprotolytic reactions in the systems immobilized on silica with a cationic
polyelectrolyte
Abstract
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 fixation 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 significant shift in pKa*
is observed. The possibility of a flow-through acidity sensor using the ratio
of the intensities of the fluorescence bands of the protonated and deprotonated
forms of the indicator is shown.
Key words: acid-base indicators, optical pH
sensors, photoinduced proton transfer, sulphonated derivatives of 2-naphthol,
organic dyes, cationic polyelectrolyte.
Copyright (C) Chemistry Dept., Moscow State University, 2002
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