title: Structural chemistry of polycyclic heteroaromatic compounds. Part 13. Photoelectron spectra and electronic structures of tricyclic hetarenes of the anthracene type.
abstract: The ultraviolet photoelectron spectra of two tricyclic heteroaromatic compounds (2,3) that are pi-isoelectronic with anthracene (1) have been recorded and analysed making use of semi-empirical AM1 and PM3, as well as density functional theory (DFT) B3LYP calculations. In compounds 2 and 3, one peripheral benzene ring of compound 1 is substituted by a thiophene ring that is either [b]- or [c]-annellated. In compounds 2 and 3, only small shifts are found for most of the ionization potentials of pi electrons. Since the ionization energies of all occupied pi molecular orbitals of compounds 1-3 could be assigned, a direct comparison of their pi electron energy is possible. Compared with compound 1, the pi-electron system of naphtho[2,3-b]thiophene (2) is stabilized by 0.6 eV, while that of naphtho[2,3-c]thiophene (3) is destabilized by 0.2 eV. [b]-Annellation of the thiophene ring is thus favourable while [c]-annellation is unfavourable.
authors.affiliation: Institut für Organishe Chemie, Universität GH Essen, Germany. paul.rademacher@uni-essen.de
authors.forename: P
authors.initials: P
authors.lastname: Rademacher
authors.forename: B
authors.initials: B
authors.lastname: Kettler
authors.forename: K
authors.initials: K
authors.lastname: Kowski
authors.forename: M E
authors.initials: ME
authors.lastname: Weiss
mesh_terms: D004583:Electrons; D006358:Hot Temperature; D007536:Isomerism; D008956:Models, Chemical; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D010777:Photochemistry; D013053:Spectrophotometry; D013876:Thiophenes / Q000737:chemistry*; D014732:Vibration
chemical_list: D009281:Naphthalenes; D013876:Thiophenes; C456966:naphtho(2,3-c)thiophene; C456965:naphtho(2,3-b)thiophene