Electroluminescent fluorene-based alternating polymers bearing triarylamine or carbazole moieties in the main chain: Synthesis and properties

Abstract

Two soluble conjugated polyfluorenes, poly{9,9-dioctylfluorene-2,7-diyl-co-4,4′-bis[2-(4-phenyl)-2-cyanovinyl]triphenylamine}(PF-BCT) and poly{9,9-dioctylfluorene-2,7-diyl-co-3,6-bis[2-(4-phenyl)-2-cyanovinyl]-9-octyl carbazole}(PF-BCC), have been synthesized from 2,7-dibromo-9,9-dioctylfluorene and 4,4′-bis[2-(4-bromophenyl)- 2-cyanovinyl]triphenylamine or 3,6-bis[2-(4-bromophenyl)-2-cyanovinyl]-9-octyl carbazole comonomers through a Suzuki polymerization reaction. The copolymers are characterized by gel permeation chromatography, elemental analysis, thermogravimetric analysis. The polymers have good thermal stability with 5 wt % loss temperatures of more than 380°C. Cyclic voltammetry measurements show that the polymers present good electron and hole-injection abilities. PF-BCC possesses higher oxidization potential than that of PF-BCT, which indicates that PF-BCT has better hole injection ability. The photophysical properties of the polymers are investigated in both solutions and spinning-coated films. Compared to that of PF-BCC, the absorption and emission peaks of PF-BCT bathochromic shift in the solid film or solution states. Single layer light-emitting devices have been fabricated in the ITO/PEDOT: PSS/polymer/Ca/Al configuration. The electroluminescence (EL) device based on PF-BCT shows yellow emission with the current efficiency of 0.21 cd/A, while PF-BCC shows greenish yellow emission with the current efficiency of 0.08 cd/A. In addition, to improve the electroluminescence of PF-BCC, a PVK layer is introduced, the brightness and efficiency get improved to 700 cd/m2 and 0.12 cd/A, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009