Electronic structure of some conjugated polymers for electron transport

The chemical and electronic structure of three different, strictly alternat ing copolymers, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NH P), poly(2,5-diheptyl-1,4-phenylene-alt-2,6-naphthylene) (P26NHP) and poly( 2,5-diheptyl-1,4-phenylene-alt-9, 10-anthrylene) (PB10AHP), have been studi ed by photoelectron spectroscopy and optical absorption spectroscopy. The e xperimental results have been analyzed using the results of quantum chemica l calculations. In the geometrical structure of all three of the polymers t here are large torsion angles between the phenylene unit and the naphthylen e or anthrylene units. These large torsion angles lead to localization of t he pi -electron wave functions, and minimal conjugation along the polymer b ackbone. For all three polymers, the highest occupied molecular orbital is completely localized to the naphthylene or anthrylene unit. The frontier mo lecular orbital wave functions are very reminiscent of the highest occupied orbitals of the isolated naphthalene or anthracene molecules. The optical absorption spectra of all three polymers verify the existence of large opti cal band gaps, consistent with the large torsion angels. The first several optical transitions in the polymers are also very reminiscent of the transi tions in single naphthalene and anthracene molecules. (C) 2001 Elsevier Sci ence B.V. All rights reserved.