Localized states in anthrylpolyenes : influence of geometry

Combining group theoretical arguments and (extended) Huckel calculations. it is shown that terminally anthryl-substituted polyenes exhibit states almost completely localized at the substituents. These localized states are related to characteristic optical transitions in anthracene which also are observed in anthrylpolyenes independent of the length of the polyene chain. substituents. I • 2 For anthrylpolyenes, characteristic changes in the absorption spectra depending on the substitution position of the anthracene have been observed. Further experimental details are presented and related to theory. In the next section the electronic states and their localization behaviour for the anthracene molecule are con­ sidered. We calculate the energy and eigenstates of the system in the Huckel approximation and show that from a group theoretical point of view this 0748-7891/90/010051-10 $05.00 :£' 1990 by John Wiley & Sons, Lid. treatment is sufficient for a qualitative description of the observed phenomena. Then the whole molecule is calculated in the Huckel approxima­ tion and the localization behaviour of the eigen­ functions for different coupling points of the chain to the anthracene is discussed. The two subsequent sections summarize the results of an extended Huckel calculation and show the in­ fluence of the geometry on energy and eigenvec­ tors of the molecule. A closer inspection using a more involved MNDO calculation shows that the geometry of the molecule under investigation is already predicted correctly within the framework of extended Huckel calculations, thus allowing us to restrict ourselves in the present context to this easier and more transparent approach. In the Experimental and Results sections absorption spectra of anthrylpolyene with variable length of the polyene chain are discussed with respect to the theory.