Excitons in Short-Chain Polydiacetylene Molecules

Abstract

We report on theoretical calculations concerning the first optically excited states of short-chain polydiacetylene (PDA) molecules. The dimer, trimer, tetramer etc. PDA molecules are obtained as reaction intermediates in the solid state polymerization reaction of diacetylene single crystals [1]. In a former Hückel-type calculation [2] we have been able to explain the ESR spectra of the triplet diradical and dicarbene states in terms of a butatriene-to-acetylene transition of the planar conjugated carbon backbone. In this contribution,an exciton theory is presented to explain the chainlength dependence and the butatriene-to-acetylene transition observed in the optical absorption spectra [3] of short-chain PDA molecules.