Theory of the radical-electron configurations and optical excitations in short-chain polydiacetylene oligomers

The chain-length-dependent radical-electron structure of short polydiacetylene chains is calculated using a configuration model. The butatriene-to-acetylene transition and a change from diradicals to dicarbenes as a function of chain length is described. By introduction of coupled electronic two-level systems a one-dimensional Frenkel exciton theory is applied for an explanation of the chain-length-dependent uv-absorption spectra. The theoretical results are in good agreement with the experimental observations.