STRUCTURAL CHEMISTRY OF POLYCYCLIC HETEROAROMATIC-COMPOUNDS .9. PHOTOELECTRON-SPECTRA AND ELECTRONIC-STRUCTURES OF ANELLATED CARBAZOLES - EXTENSION OF CLAR AROMATIC SEXTET MODEL TO HETARENES

The photoelectron spectra of carbazole (1), 9-methylcarbazole (2), ben zo- and dibenzocarbazoles (3-7, 15), naphthocarbazoles (8, 9), benzona phthocarbazoles (10-12), and dinaphthocarbazole (14) are reported. Bas ed on HAM/3 and AM1 calculations, the ionization potentials are assign ed to molecular orbitals. Close relationship of the electronic structu res of the anellated carbazoles and the corresponding pi-isoelectronic arenes is observed; ionization potentials for most pi-electrons devia te by less than 0.2 eV. Analysis of the PE spectra of isomeric carbazo les leads to an extension of Clar's aromatic sextet model to hetarenes , which can explain the correlation between relative stabilities and f irst ionization potentials.