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

We investigate the dependency of the electronic structure of methyl and pyridine substituted anthrylpolyenes on the polyene chain length. A systematic analysis of the experimental absorption spectra reveals a remarkable complexity of the electronic properties of the supermolecules. Mixed absorption bands are observed that cannot be assigned to transitions of the individual molecular components. Ground state semiempirical calculations show that the fragment's molecular orbital symmetries are partially preserved due to a twisted biplanar molecular structure. 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 electronic properties are reproduced quantitatively with regard to its dependency on chain length, state mixing and substitution effects.