Spectral Characteristics of Phenylenediamines and Their Various Protonated Species

Increase in the Stokes shift [νabs(max)−νflu (max)] with an increase in the polarity and hydrogen-bonding capacity of the solvents is the maximum for p-phenylenediamine and the minimum for m-phenylenediamine. These studies have indicated that the two amino groups in o- and p-phenylenediamines are not in the same plane of the benzene ring. Spectral characteristics of monocations and dications resemble to those of aniline and benzene respectively. pKa values for the dication–monocation and monocation–neutral equilibria have been determined, both in S0 and S1 states, and discussed.