Defect electronic states in beta -carotene and lower homologues

The authors present semi-empirical calculations of the atomic geometries and electronic charge distributions of beta -carotene homologues of different chain lengths. They find defects in charged and photoexcited chains that are similar to the defects found in the degenerate polymer transpolyacetylene, and show how confinement affects these defects as the chains are shortened. The results exhibit a generalized form of charge-conjugation symmetry in which the properties of a negatively charged defect are related to those of a positive one and vice versa.