Vibronic properties of 2-azaanthracene and its derivatives

We report an experimental and theoretical (PPP method) study of the UV absorption spectra of 2-azaanthracene and four of its methyl-substituted derivatives. We find that the p bands of these compounds consist of two different vibronic ππ* bands. Our experimental and theoretical results suggest a rule for evaluating the effect of methyl groups on π →π* transition energies as a function of the π charge on the atoms. We interpret the reasons for the different effects of a polar solvent and hydrogen bonding on the ππ* bands of these compounds. © 1978 Plenum Publishing Corporation.