Electroluminescence of organic thin films based on blends of polystyrene and fluorescent dyes

Blue and red light-emitting diodes were constructed as devices in which a polystyrene/dye blend was sandwiched between a calcium electrode and a transparent indium-tin oxide electrode. As dye molecules, four alkoxy-substituted derivatives of 2,5-dialkoxy-1,4-bis(2-phenylvinyl)benzene (i.e. p-phenylene vinylene oligomers), a derivative of bisanthracene (2,2′,3,3′-tetrachloro-9,9′-dimethoxy-10,10′-bianthracene) and the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminophenylvinyl)-4H-pyran (DCM) were used. The critical field for light emission in devices using 20 wt.% PPV oligomers in polystyrene was found to be of the order of 2 × 108 V m–1. The dependence of the device conductivity on the concentration of dye molecules in the polystyrene film is described by simple percolation theory. The synthesis of 2,2′,3,3′-tetrachloro-9,9′-dimethoxy-10,10′-bianthracene is reported.