Blue-light-emitting oligoquinolines: Synthesis, properties, and high-efficiency blue-light-emitting diodes

The synthesis, photophysics, cyclic voltammetry, and highly efficient blue electroluminescence of a series of four new n-type conjugated oligomers, 6,6'-bis(2,4-diphenylquinoline) (BIPPQ), 6,6'-bis(2-(4-tert-butylphenyl)-4-phenylquinoline) (BtBPQ), 6,6'-bis(2-p-biphenyl)-4-phenylquinoline) (B2PPQ), and 6,6'-bis((3,5-diphenylbenzene)-4-phenylquinoline) (BDBPQ) is reported. The oligoquinolines have high glass-transition temperatures (T-g >= 133 degrees C, reversible electrochemical reduction, and high electron affinities (2.68-2.81 eV). They emit blue photoluminescence with 0.73-0.94 quantum yields and 1.06-1.42 ns lifetimes in chloroform solutions. High-performance organic light-emitting diodes (OLEDs) with excellent blue chromaticity coordinates are achieved from all the oligoquinolines. OLEDs based on B2PPQ as the blue emitter give the best performance with a high brightness (19 740 cd m(-2) at 8.0 V), high efficiency (7.12 cd A(-1) and 6.56% external quantum efficiency at 1175 cd m(-2)), and excellent blue color purity as judged by the Commission Internationale de L'Eclairage (CIE) coordinates (x = 0.15, y = 0.16). These results represent the best efficiency of blue OLEDs from neat fluorescent organic emitters reported to date. These results demonstrate the potential of oligoquinolines as emitters and electron-transport materials for developing high-performance blue OLEDs.