A study of the molecular structure and spectroscopic properties of benzo- and pyrido-tetraazapentalenes Original Research Article

The equilibrium structures of Y- and Z-dibenzotetraazapentalene and some pyridyl derivatives were fully optimized by the density functional method B3LYP/6-31+G(d,p). For all the molecules, the results predict a fully conjugated planar geometry. The NMR 13C chemical shifts were recorded and analyzed by means of ab initio continuous set of gauge transformations calculations performed with the B3LYP/6-311+G(2d,p) DFT–HF hybrid model, which account for the different displacements of the resonances in the NMR spectra. The He(I) photoelectron spectra were measured and interpreted by means of ab initio outer valence Green function calculations, which give an overall consistent description of the energies, sequence and splitting of the uppermost bands. These are mainly associated with the π and n(N) orbitals of the central tetraaza fragment and with the n(N) lone pairs of the pyridyl rings. Electron transmission spectroscopy was employed to characterize the low-lying temporary anion states of the Y- and Z-isomers.