Synthesis and characterization of poly(fluorene)‐based copolymers containing various 1,3,4‐oxadiazole pendants

A series of soluble alternating poly(fluorene)‐based copolymers containing electron‐transporting 1,3,4‐oxadiazole (OXD) and hole‐transporting carbazole pendants attached to the C‐9 position of fluorene units by long alkyl spacers were synthesized. These copolymers possess mesogenic and nonmesogenic pendants attached to a rigid mesogenic poly(fluorene) (PF) backbone. All these polymers exhibit glass‐forming liquid crystalline properties, including the nematic and smectic A (SmA) phases, and reveal much wider mesophasic temperature ranges than that of PF. The thermal properties and mesomorphism of these conjugated polymers are mainly affected by the nature of these pendants, and thus the mesophasic temperature ranges and glass‐forming properties are greatly enhanced by introducing the OXD pendants. In addition, the tendencies of crystallization and aggregation of PF are also suppressed by introducing the OXD pendants. A single layer device with P4 as an emitter shows a turn‐on voltage of 5 V and a bright luminescence of 2694 cd/m² at 11 V with a power efficiency of 1.28 cd/A at 100 mA/cm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2700–2711, 2005