Efficient cyano-containing electron-transporting polymers for light-emitting diodes

Two copolymers composed of 9,9-di-n-hexylfluorene and 2,5-dicyanobenzene (PF-CNP (3:1) and PF-CNP (1:1)) were synthesized via the Suzuki coupling reaction. By attaching two electron-withdrawing cyano groups onto the phenylene ring, the electron affinity and conduction of polyfluorenes are greatly enhanced. The device based on PF-CNP (3:1) has a low turn-on voltage (3.4 V), bright blue emission (5430 cd/m(2) at a bias voltage of 7.4 V), and a maximum external quantum efficiency of 0.50% due to both optimized electron affinity and conduction.