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Better blue for polyfluorene OLEDs Polyfluorenes are a leading candidate for blue organic light-emitting diodes (OLEDs) that, along with green- and red-emitting materials, are expected to be part of the first full-color polymer displays. One challenge for the use of polyfluorene has been minor chemical defects in the polymer that give rise to an interfering green emission band, which affects color purity. A team of researchers at Eindhoven University of Technology and Philips Research Laboratories in the Netherlands has now developed a simple purification procedure to make higher quality polyfluorene that doesn’t exhibit the green band [J. Mater. Chem., published online, http://www.rsc.org/is/journals/j1.htm (DOI: 10.1039/b308402g)]. The team dissolved 2,7-dibromo-9,9-di[(S)-3,7-dimethyloctyl] fluorene monomer in tetrahydrofuran with potassium tert-butoxide. The base deprotonates any fluorene molecules that are not fully alkylated at the 9-position. Subsequent filtering allows the insoluble impurities to be removed, and the pure monomer is recovered from the solvent. Although there’s no spectroscopic difference between monomer treated with or without the new step, the polymer (shown) prepared from the purified monomer doesn’t have the green emission band |
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