The electronic spectrum of 1, 4, 5, 8-tetraazanaphthalene Original Research Article

Electronic spectra of 1, 4, 5, 8-tetraazanaphthalene (1458-TAN) have been recorded in solution, durene mixed crystals, stretched polymer films and solid argon matrices, and analysed using semiempirical CNDO/S-CI and ab initio CIS/3-21G calculations. Earlier predictions of a symmetry-forbidden π∗ ← n transition at long wavelengths are confirmed, and support long-standing predictions of strong through-bond interactions involving n-type molecular orbitals. A second and symmetry-allowed π∗ ← n transition is thought to be swamped by strong π∗ ← π absorption. The vibronic structure of the first π∗ ← π band system near 32 000 cm−1 has been analysed, and higher-energy absorption bands have been tentatively correlated with several other π∗ ← π and π∗ ← n transitions. Although 40% of the ring atoms in 1458-TAN are nitrogens, the absorption spectrum of the compound resembles the spectra of less highly substituted azanaphthalenes.