Excited state reactions of some aromatic carbonyl compounds

Abstract

The pK values for xanthone protonation in the S₀, S₁ and T₁ states have been determined by direct measurement and by Forster Cycle calculation. Both methods for determining pK give the order for xanthone of pK(T₁) > pK(S₁) > pK(S₀). A study of benzophenones and acetophenones showed this pK order to be a common one for aromatic carbonyl compounds. The pK order for these compounds has been explained in terms of the type of transitions involved and the S₁-T₁ splitting of these transitions. In the case of substituted aromatic carbonyl compounds the pK order reflects the effect of substitution on the lowest S₀-S₁ and transitions. Results are also presented on the effect of inorganic anions solvenli and temperature on xanthone fluorescence. Spectral details are reported for several xanthones, benzophenones, acetophenones, and anthraquinones.