Electronic absorption spectra of dibenzotetraazaannulenes: Effect of periphery substituents

In this work, the authors resolved the electronic absorption spectra of three tetraazaannulenes of different symmetry measured in solution at 298 and 77 K. The results obtained allowed assignation of the bands observed in the visible region to n → π* transitions and to vibronic components of two π → π* transitions. The efficiency of vibronic interaction is shown to depend on the molecular symmetry and reflects synchronized-desynchronized exchange of hydrogen atoms between nitrogen atoms in a macrocycle. 20 refs., 3 figs., 1 tab