Electroluminescent Polymers Containing Rare Earth Metal Complexes

In this work, two rare earth (RE) metal complex monomers Eu(MAA)(BA)2(Phen) and Tb(MAA)(acac)2(Phen) were designed and synthesized. They were copolymerized with methylmethacrylate (MMA) and hole-transporting N-vinylcarbazole (NVK) to give a novel RE-containing ternary copolymer PKMTbEu. Electron-transporting oxadiazole monomer 2-phenyl-5-(p-(N-acrylate)amino-phenyl)-1,3,4-oxadiazole (DPO) was designed, synthesized and copolymerized with NVK, MMA and Tb(MAA)(acac)2(Phen) to give a Tb-complex containg copolymer PKMOTb with dual transporting moieties. The copolymer structure was characterized with IR, UV-vis and AFM. Photoluminescence (PL) was used to study the photophysical properties of the copolymers. Two single -layer light emitting diodes (LED) were fabricated based on the two copolymers (PKMTbEu and PKMOTb) by solution spin coating, with 1TO as anode and Al as cathode. Their electroluminescent performance was investigated.PL spectrum of PKMTbEu shows carbazole's emission as a broad band between 340nm and 460nm; and shows the RE metal ion's sharp emission peaks centered at 545nm and 617nm as generated from 4f electronic transition in Tb3+ and Eu3+ respectively. The excimer emission from partially-overlap carbazole groups and totally-overlap carbazole groups was observed. Long-range excited energy transfer from carbazole to RE complexes was observed through static PL investigation. The color tunability of the polymer was investigated by examining PL spectra of PKMTbEu obtained with different RE complex monomers feed ratio. The current-voltage and EL characteristics of LED ITO/PKMTbEu/Al were investigated, and the device's possible work mechanism was also proposed. A blue emitter N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) was doped into PKMTbEu to allow the fabrication of a single layer white light emitting LED: ITO/PKMTbEu:TPD/Al. The standar chroma coordinator of this white light emitting LED's was calculated.The carbazole emission and oxadiazole emission were observed from the PL spectrum of PKMOTb. Energy transfers from both carbazole and oxadiazole moieties to terbium complex were compared by means of photoluminescence. The single layer device ITO/PKMOTb/Al has a turn on voltage as low as 6.2V, which was explained by analyzing the energy level of PKMOTb. The device shows a monochromaticemission characterized as Tb3+ ion's 4f electronic transition, and the excited energygenerated on carbazole and oxadiazole was believed as quenched by energy transfer.