Transient Photochemistry of Safranin-O.
Interim technical rept.,
RENSSELAER POLYTECHNIC INST TROY N Y DEPT OF CHEMISTRY
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We have characterized the spectra, acidity constants and decay kinetics of the triplet and semireduced radical species of Safranin-O. Between pH 3.0 and pH 10.6 there are three triplet species denoted 3DH22, 3DH and 3D, the pKsub as being 7.5 and 9.2. All three triplet species exhibit first order decay, the rate constant for 3DH22 being circa 5-fold lower than the rate constants of 3DH and 3D. Ascorbic acid and ethylenediaminetetraacetic acid quench the triplet state under appropriate pH conditions and the pH dependencies of the yield of semireduced dye indicate that 3DH22 is more reactive than 3DH or 3D. With ethylenediaminetetraacetic acid as reducing agent, there is the additional requirement that at least one of the amino nitrogens be deprotonated to obtain a significant yield of semireduced dye. In these reactions, ascorbic acid is oxidized reversibly, but ethylenediaminetetraacetic acid is oxidized irreversibly, so that with the latter reducing agent photolysis causes buildup of the leucodye, which on subsequent photolysis can reduce triplet state dye. With ascorbic acid as reducing agent, the regeneration of the ground state dye is reversible, the decay of the semireduced radical being second order.
- Organic Chemistry
- Atomic and Molecular Physics and Spectroscopy