Effect of the Basic Strength of Attached Groups on Light Absorption Spectra, IV. Proton Dissociations of Some Aromatic Molecules in Their Excited State

Abstract

A general standard of the classification is given for the acid-base character of some aromatic molecules with special reference to the change of the character after and before the first excitation. The criterion is Δq\gtreqqless0, Δq being the change in the π-electron density of the special member of the attached group after and before the excitation. This corresponds to pK_a1\lesseqqgtrpK_a2 where pK_a1 and pK_a2 are the proton dissociation constants in the ground and the excited state respectively. Examples are the case of acridon cation which gives Δq=0.099 corresponding to pK_a2−pK_a1=2.48 (observed value 2.6) and the case of 3-oxyacridine which gives Δq=−0.18 corresponding to pK_a2−pK_a1=−4.52 (observed value, if any, −5.27). Though the cases of naphthylamine and naphthol were treated in the previous paper III, some corrections about the term values and the discussion of the paper III are given in the present paper.