Lubica Klicova, Peter Sebej, Tomas Solomek, Bruno Hellrung, Petr Slavicek, Petr Klan, Dominik Heger, Jakob Wirz, "Adiabatic Triplet State Tautomerization of p-Hydroxyacetophenone in Aqueous Solution", J. Phys. Chem. A, 2012 116, 2935-2944.

Abstract: The primary photophysical processes of p-hydroxyacetophenone (HA) and the ensuing proton transfer reactions in aqueous solution were investigated by picosecond pump-probe spectroscopy and nanosecond laser flash photolysis. Previous studies have led to mutually inconsistent conclusions. The combined data allow us to rationalize the excited-state proton transfer processes of HA in terms of a comprehensive, well-established reaction scheme. Following fast and quantitative ISC to the triplet state, 3HA*, adiabatic proton transfer through solvent water simultaneously forms both the anion, 3A-*, and the quinoid triplet enol tautomer, 3Q*. The latter subsequently equilibrates with its anion 3A-*. Ionization and tautomerization are likely to compete with the desired release reactions of p-hydroxyphenacyl photoremovable protecting groups.