Excimer luminescence from single crystals and films of a cyano-substituted phenylene–vinylene model compound Original Research Article

In the context of luminescence from the solid state of poly(para-phenylene vinylene)-type materials, we report a study of three octyloxy-substituted five-ring oligo(para-phenylene vinylene)s, two of which bear cyano substituents on the innermost vinylene bonds. For each compound, the molecular arrangement in the single crystal has been derived from a crystallographic analysis. For the compound which has the cyano group not directly adjacent to the central ring, synthesis and structure are described here in detail. This compound, in contrast to the other two, has molecular π-stacking in the crystal lattice. Only for this compound do we observe a strongly red-shifted, long-lived emission, which is therefore ascribed to an excimer-type intermolecular excitation. The observations of excimer-type emission from cyano-substituted alkoxy–PPVʹs and in related copolymers fit in very well with the molecular picture derived from this study of model compounds.