STRUCTURAL CHEMISTRY OF POLYCYCLIC HETEROAROMATIC-COMPOUNDS .7. PHOTOELECTRON-SPECTRA AND ELECTRONIC-STRUCTURES OF THIENONAPHTHYRIDINES .1.

The He(I) photoelectron spectra of twelve isomeric thienonaphthyridine s (1-12) are reported. Based on PM3 calculations, the ionization poten tials (IP) have been assigned to molecular orbitals. The electronic st ructures are discussed according to first order perturbation theory. I n particular, the effects of nitrogen lone pair interactions in the na phthyridine fragments on ionization potentials are investigated. Posit ional effects of the two nitrogen atoms are reflected in the energies of the pi MOs and in the separation of the two n(N) orbitals. The mode of annelation of the thiophene ring has a distinct effect on the ener gy of the first IP.