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 wid ely used classes of phosphors in light emitting diodes. Central problems ar e the imbalanced charge carrier injection and transport properties due to t he high lying conduction band. A series of good soluble oligo(phenyleneviny lene)s (OPV) with five benzene rings and a variety of electron withdrawing and accepting substituents have been prepared and may serve as model compou nds for PPV with increased electron affinity. The central ring of the OPVs is substituted with two octyloxy groups to ensure good solubility and the l ateral styrene units carry further chromophoric groups of different electro nic character. The synthesis was performed via Horner olefination and Knoev enagel condensation. The electronic spectra of these OPVs are dominated by the main chromophore, further auxochrome groups on the lateral rings (m- an d p-positions) shift absorption and emission spectra only slightly to longe r wavelengths. Significant bathochrome shifts are observed for OPVs with cy ano-groups on the terminal vinylene segments. The OPVs are photochemical st able versus irradiation with NUV whereas MUV and traces of acids cause deco mposition of the chromophore. (C) 2000 Elsevier Science S.A. All rights res erved.