"Click" Synthesis of a Bipolar Dendrimer as a Host Material for Electrophosphorescent Devices

A new solution‐processable bipolar dendrimer with carbazole units as hole‐transporting units and oxadiazole units as electron‐transporting units was efficiently synthesized based on a convergent approach by alternation of a Cu‐catalyzed azide/alkyne cycloaddition reaction and Williamson ether synthesis. The orthogonal chemistry completely avoided protection and activation of the focal points in the process of dendrimer synthesis. The dendrimer showed a wide bandgap and good thermal stability. Electrophosphorescent devices with the configuration ITO/PEDOT:PSS/bipolar dendrimer:Ir(ppy)3/TPBI/LiF/Al were fabricated. The devices showed a maximum current efficiency of 16.8 cd · A−1, a maximum power efficiency of 4.22 lm · W−1 and an external quantum efficiency of 5.7%. A new bipolar dendrimer 4CZ–(CH2)6–4OXZ is synthesized by combining the CuAAC “click” reaction with Williamson ether synthesis. The convergent strategy and orthogonal coupling method are shown to be highly efficient. The first electrophosphorescent device based on a bipolar dendrimer with 1,2,3‐triazoles as linkers is described.