Model calculation of PDA–PA heterostructures: Quantum wells in conjugated molecular chains

The energy band structures and the corresponding eigenfunctions of polymer chain heterostructures are calculated on the basis of the Hückel theory. The model structure is given by a coupled conjugated polymer system consisting of polydiacetylene (PDA) and polyacetylene (PA) units. The PA–PDA ratio is varied from 0% to 100%. Discrete split-off states within the energy gap and at the exterior of the bands are analyzed with respect to their energies and localization of the corresponding wave function on the PA or PDA units. Criteria for one-dimensional molecular quantum well structures and molecular electronic devices are discussed.