Excited states of six-membered aza-aromatic rings. IX. 1,4- and 5,12-diazatriphenylenes

Abstract

The two isomeric diazatriphenylenes, 1,4-DAT and 5,12-DAT, and the corresponding singly and doubly protonated forms were investigated in the ground state, phosphorescent state and fluorescent state by the methods of electronic spectroscopy, ESR spectroscopy and quantum chemistry. The following properties were measured: (π, π ∗) excitation energies, acid-base equilibrium constants, quantum yields of fluorescence, lifetimes and zero-field splitting parameters of the triplet states, for the bases and the conjugate acids. The results of semi-empirical calculations performed using the PPL LCI SCF method based on monoexcited configurations were compared with experimental data. The calculated electron densities on nitrogen were correlated with pK's for the two equilibria and the three electronic states. The unusually large increase of pK (by about six units) of the triplet 1,4-DAT, has been found and interpreted. A very good correlation of zero-field splitting parameter D 1 3 versus singlet-triplet splitting was obtained.