The electronic spectrum of 1,4,5,8-tetraazanaphthalene

Electronic spectra of 1,4,5,8-tetraazanaphthalene (1458-TAN) have been reco rded in solution, durene mixed crystals, stretched polymer films and solid argon matrices, and analysed using semiempirical CNDO/S-CI and ab initio CI S/3-21G calculations. Earlier predictions of a symmetry-forbidden pi* <-- n transition at long wavelengths are confirmed, and support long-standing pr edictions of strong through-bond interactions involving n-type molecular or bitals. A second and symmetry-allowed pi* <-- n transition is thought to be swamped by strong pi* <-- pi absorption. The vibronic structure of the fir st pi* <-- pi band system near 32000 cm(-1) has been analysed, and higher-e nergy absorption bands have been tentatively correlated with several other pi* <-- pi and pi* <-- n n transitions. Although 40% of the ring atoms in 1 458-TAN are nitrogens, the absorption spectrum of the compound resembles th e spectra of less highly substituted azanaphthalenes. (C) 1999 Elsevier Sci ence B.V. All rights reserved.