Soluble oligo(phenylenevinylene)s with electron withdrawing substituents for the use in light emitting diodes

Poly(p-phenylenevinylene) (PPV) and its derivatives are one of the most widely used classes of phosphors in light emitting diodes. Central problems are the imbalanced charge carrier injection and transport properties due to the high lying conduction band. A series of good soluble oligo(phenylenevinylene)s (OPV) with five benzene rings and a variety of electron withdrawing and accepting substituents have been prepared and may serve as model compounds for PPV with increased electron affinity. The central ring of the OPVs is substituted with two octyloxy groups to ensure good solubility and the lateral styrene units carry further chromophoric groups of different electronic character. The synthesis was performed via Horner olefination and Knoevenagel condensation. The electronic spectra of these OPVs are dominated by the main chromophore, further auxochrome groups on the lateral rings (m- and p-positions) shift absorption and emission spectra only slightly to longer wavelengths. Significant bathochrome shifts are observed for OPVs with cyano-groups on the terminal vinylene segments. The OPVs are photochemical stable versus irradiation with NUV whereas MUV and traces of acids cause decomposition of the chromophore. (C) 2000 Elsevier Science S.A. All rights reserved.