LINEAR DICHROISM OF ACENAPHTHO[1,2-K]FLUORANTHENE AND ITS 7,14-DIPHENYL AND 7,14-DICARBETHOXY DERIVATIVES

The linear dichroism spectra of acenaphtho[1,2-k]fluoranthene, 7,14-di phenylacenaphtho[1,2-k]fluoranthene, and 7,1 4-dicarbethoxyacenaphtho[ 1,2-k]fluoranthene in stretched polyethylene sheet at room temperature were measured. The electronic transition energies and transition mome nt directions were computed by semiempirical PPP SCF CI and ZINDO calc ulations and compared to the experimentally determined values. A high degree of similarity to the electronic transitions in fluoranthene is found. At least six electronic transitions are assigned on the basis o f the linear dichroism spectra. The phenyl and carbethoxy substituents produce only a minor perturbation of the experimental spectroscopic t ransitions. These results are consistent with data that show that the orthogonality of the substituents prohibits their significant conjugat ion with the parent molecule. The orientation of the compounds in the stretched sheet is discussed.