Aromatic polyethers with oxadiazole units - synthesis and application in organic light emitting diodes

Detailed synthetic aspects of new aromatic polyethers containing oxadiazole units are described. They are obtained by the nucleophilic displacement reaction of 2,2-bis(4-hydroxyphenyl)hexafluoropropane with 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole and 2,5-bis(4-fluoronaphthyl)-1,3,4-oxadiazole. The purity of the polyethers strongly depends on the reaction solvent. Best results were achieved with Ph2SO2 as compared to N-methyl-2-pyrrolidone (NMP) and 1,3-dimethyltetrahydro-2(1H)-pyrimidinone (DMPU) in the temperature range from 190-200 degrees C. All polyethers are fully soluble in common organic solvents and excellent films are obtained by spin-coating. High molecular weight polyethers without oligomers were only achieved, when Ph2SO2 was used as solvent. All polyethers are characterized by high thermal stability and high glass transition temperatures. The substitution of bisphenyloxadiazole by bisnaphthyloxadiazole units in the polyethers leads to a bathochromic shift of the absorption from 299 nm to 345 nm. Poly ethers with bisnaphthyloxadiazole units show a blue fluorescence with a maximum at 427 nm. The application of these novel polyethers as efficient electron transport and injection layer in bilayer light emitting diodes based on poly(1,4-phenylenevinylene) is shown. The best results were obtained with oxadiazole polyethers containing bisnaphthyloxadiazole units.