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ONE EXAMPLE is a materials application presented by chemistry professor James M. Boncella of the University of Florida. Boncella's group has been working with the groups of Florida chemistry professors John R. Reynolds and Kirk S. Schanze to prepare electroluminescent lanthanide complexes containing Tp ligands. The researchers are incorporating the complexes in the active layer of polymer light-emitting diodes (PLEDs). In a new series of lanthanide complexes described by Boncella, a Tp ligand binds the top half of the lanthanide metal and a tetraphenylporphyrin ligand binds the lower half, encapsulating the lanthanide(III) ion and shielding it from outside interactions. The researchers are finding that the seven-coordinate complexes with Pr, Nd, Ho, Er, Tm, and Yb have enhanced luminescence efficiencies compared with mono- or bidentate ligands, he said. The Florida chemists have constructed multilayer PLEDs in which the active layer is a 2:1 blend by weight of a lanthanide complex and polystyrene or an alkoxy-substituted poly(p-phenylene), Boncella explained. When a voltage is applied to the PLED, the conjugated polymer transfers energy to the lanthanide metal center through the porphyrin, which leads to emission of near-infrared light in the range of 980 to 1,700 nm, depending on the metal used. "Although the quantum yields of the devices are low at 0.1%," Boncella said, "they still produce enough light to be easily seen without specialized equipment." The researchers are tinkering with various metal-ligand-polymer combinations to tailor the performance of the PLEDs, he noted. "There is a laundry list of potential applications," Boncella stated, "ranging from telecommunications, sensors, biomedical uses, and defense applications such as night vision." |
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