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, wh ich contains additional segments of 2-phenyl-5-(4-biphenyl)- 1,3,4-oxa diazole (PBD) groups in the polymer main chain. The PBD segments and t he ladder-type copolymer segments act as independent conjugated system s. Electroluminescent devices show electric properties comparable with ladder-type para-phenylene copolymers without PBD groups. We find evi dence 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.