Structural chemistry of polycyclic heteroaromatic compounds. Part XI. Photoelectron spectra and electronic structures of tetracyclic hetarenes of the triphenylene type.
In: Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (Spectrochim.Acta, Pt.A: Mol.Biomol.Spectrosc.), Jg. 56A (2000) ; Nr. 6, S. 1179-1190
Zeitschriftenaufsatz / Fach: Chemie
The UV photoelectron spectra of several tetracyclic heteroarom. compds. (2-9 = II-IX) which are p-isoelectronic with triphenylene (1) have been recorded and analyzed making use of semiempirical AM1 and PM3 as well as ab initio/DFT B3LYP calcns. In one series of compds. (2-7), the peripheral benzene rings of 1 are successively substituted by thiophene rings that are either [b]- or [c]-annelated with the central benzene unit. In 2-7 only marginal shifts are found for most of the IPs of electrons. In the benzotrithiophenes 5-7, a systematic variation is displayed by IP(p7). Compared to 1, the p electron system of benzo[c]trithiophene (7) is approx. two times as much destabilized as in the isomers 5 and 6 with [b]annellated thiophene rings. The IP[n(S)] values of the thiophene derivs. 2-7 indicate that these orbitals are clearly destabilized relative to thiophene. The same holds for the n(O) orbital of the furan deriv. 9 in comparison with that of furan. In 9, only the higher p MOs (p7-p9) are destabilized whereas the lower levels (p1-p4) are stabilized, and those in between (p5-p6) remain essentially unshifted. In the pyrrole deriv. 8, all p MOs are substantially destabilized by about 0.5-1.6 eV relative to 1.