Synthesis, Photophysics, Theoretical Modeling, and Electroluminescence of Novel 2,7-Carhazole-Based Conjugated Polymers with Sterically Hindered Structures

2,7-dibromo-N-hexylcarbazole is successfully synthesized in three steps with an overall 37% yield. Novel 2,7-carbazole-based sterically hindered conjugated polymers are further synthesized. In the backbone structure of polymer P1, alkylated bithiophene moiety is beta-substituted with dodecyl chains on both thiophene rings, adopting the tail-to-tail configuration. While for polymers P2 and P3, partially planarized thieno[3,2-b]thiophene moiety (P2) and beta-pentyl substituted thieno[3,2-b]thiophene (P3) are incorporated. All polymers demonstrate efficient blue-to-green light emission, good thermal stability (T-d >= 379 degrees C), and high glass transition temperatures (T-g = 118 degrees C). The optical and electronic properties of the resulted polymers are tuned by the incorporated alkyl chains. For instance, the incorporation of I-pentyl group in thieno[3,2-b]thiophene moiety endows P3 with blue-shifted photophysical spectra, reduced fluorescence quantum yield and larger band gap in comparison with P2. The steric effect of incorporated alkyl chains is further illustrated by geometry optimization of three model oligomers (analogues to the repetition units of P1-P3) using density functional theory. Sterically hindered polymers P1 and P2 exhibit high charge transport ability and moderate electroluminescent properties in primarily tested single-layer light-emitting diodes (configuration: ITO/PEDOT:PSS/Polymer/Ca/Ag). (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7725-7738, 2008