A blue-luminescent ladder-type poly(para-phenylene) copolymer containing oxadiazole groups

We report investigations of electroluminescence and photoluminescence in a blue-luminescent soluble ladder-type para-phenylene copolymer, which contains additional segments of 2-phenyl-5-4-biphenyl)-1,3,4-oxadiazole (PBD) groups in the polymer main chain. The PBD segments and the ladder-type copolymer segments act as independent conjugated systems. Electroluminescent devices show electric properties comparable with ladder-type para-phenylene copolymers without PBD groups. We find evidence that hole transport is not reduced, and still takes place along ladder units. We measure typical internal quantum efficiencies of 0.4% with Al cathodes, which is a high value for a blue-luminescent single-layer device with air-stable electrodes.