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) (B1PPQ), 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 (Tg ≥ 133 °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.