High efficiency and small roll-off electrophosphorescence from a new iridium complex with well-matched energy levels

A new homoleptic cyclometalated iridium triplet green emitter based on a phenylpyridazine ligand was reported. Trans-1,2-dibenzoylethylene was dissolved in acetic acid by heating, An excess amount of hydrazine monohydrate was added dropwise after cooled down to room temperature. (25 ml.) was added dropwise. The reaction mixture was kept stirred at room temperature for another hour, and then refluxed overnight. After cooling down, the solution was poured into ice to obtain a white precipitate. Subsequent recrystallization from chloroform yielded the product. The starting material BPPya and Ir(acac), were dissolved in degassed glycerol (10 mL). Dark-orange colored products precipitated out gradually upon reflux at 220°C in a nitrogen environment for 10 h. The precipitate was collected by filtration, washed with hexane and ether, and finally dried in vacuum. It was proved that T-T annealing in PhOLEDs can be avoided if the energy levels of the host and the phosphorescent dopant are closely matched.