Novel poly(2,3-biphenyl-1,4-phenylenevinylene) derivatives containing long branched alkoxy and fluorenyl substituents: Synthesis, characterization, and their applications for polymer light-emitting diodes

Abstract

Two series of poly(2,3-Biphenyl-1,4-phenylenevinylene) (DP-PPV) derivatives containing long branched alkoxy chains or fluorenyl substituents were synthesized. The branched alkoxy groups were introduced to enhance the solubility for spin-coating processes. Bulky fluorenyl groups with two hexyl chains on the 9-position were introduced to increase steric hindrance and prevent close packing of the main chain. By controlling the feed ratio of different monomers during polymerization, DP-PPV derivatives with high molecular weights were obtained. All synthesized polymers possess high glass transitions temperatures and thermal stabilities. The maximum photoluminescent emissions of the thin films are located between 498 and 564 nm. Cyclic voltammetric analysis reveals that the band gaps of these light-emitting materials are in the range from 2.4 to 2.5 eV. A double-layer electroluminescent device with the configuration of ITO/PEDOT/polymer 2/Ca/Al exhibited a low turn-on voltage (4.0 V), a very high external quantum efficiency (3.39 cd/A), and a high brightness (16 910 cd/m(2)).