DONOR-ACCEPTOR SUBSTITUTED LINEAR POLYENES - CHAIN-LENGTH DEPENDENT ELECTRONIC-STRUCTURE OF ANTHRYLPOLYENES

We investigate the dependency of the electronic structure of methyl an d pyridine substituted anthrylpolyenes on the polyene chain length. A systematic analysis of the experimental absorption spectra reveals a r emarkable complexity of the electronic properties of the supermolecule s. Mixed absorption bands are observed that cannot be assigned to tran sitions of the individual molecular components. Ground state semiempir ical calculations show that the fragment's molecular orbital symmetrie s are partially preserved due to a twisted biplanar molecular structur e. A simple physical model is presented which is based on this special geometry, i.e. two partially decoupled tau-electronic subsystems are considered. Both the experimental and semiempirical data on the electr onic properties are reproduced quantitatively with regard to its depen dency on chain length, state mixing and substitution effects.