Development of efficient electron-transporting polymers for light-emitting diodes

Polyfluorenes are a class of very efficient conjugated polymers used in the development of LEDs that exhibit very high hole mobility. In order to balance the charge transport and enhance quantum efficiency of the LEDs, fluorene- based copolymers were synthesized based on the statistic copolymerization between fluorene and 2,5-dicyanobezene. By attaching two electron-withdrawing cyano groups onto the phenylene ring, both the electron affinity and the electron conduction of these copolymers are greatly enhanced comparing to the fluorene homopolymer. LED devices using the cyano-containing fluorene copolymers show very bright emission and low turn-on voltages. The emission color of these polymers could be also tuned by exciplex formation between the polymers and amine-containing hole transporting materials.