Thermal and spectral stability of electroluminescent hyperbranched copolymers containing tetraphenylthiophene-quinoline-triphenylamine moieties

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2012-01, Vol.50 (2), p.237-249
• Main Authors: Tsai, Ya-Ting, Lai, Chung-Tin, Chien, Rong-Hong, Hong, Jin-Long, Yeh, An-Chi
• Format: Article
• Language: English
• Subjects: Annealing; Applied sciences; branching density; Copolymers; Density; Electroluminescence; Electronics; Emission; Exact sciences and technology; fluorescence; high temperature materials; hyperbranched; hyperbranched copolymer; Optoelectronic devices; Organic polymers; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Quinoline; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Spectra; Stability; tetraphenylthiophene; thermal and spectral stability; triphenylamine
• ISSN: 0887-624X; 0887-6266; 1099-0518
• DOI: 10.1002/pola.25020

Fluorescent hyperbranched copolymers (HB‐x, x = 1–4) with inherent tetraphenylthiophene, triphenylamine (TPA) and quinoline (Qu) moieties were prepared to study the influence of the TPA branching point on the thermal and the spectral stability. All the HB‐x copolymers exhibited high glass transition temperatures (Tgs = 245–315 °C) with the detected values increasing with the increasing branching TPA content in the HB‐x. The solid HB‐x films possess high emission efficiency with the resulting quantum yields (ϕFs) in the ranges of 0.72–0.74. More importantly, the HB‐x copolymers and the derived light‐emitting devices exhibit high photoluminescence (PL) and electroluminescence (EL) stability towards thermal annealing at temperatures higher than 200 °C. After annealing at 200 °C (or 300 °C), no change was observed in the respective PL and EL spectra of HB‐1 (or HB‐4) copolymers. The spectral stability was found to correlate with Tg and with the highest branching density, HB‐4 copolymer possesses the highest thermal stability among all HB‐xs and show no EL spectral change after annealing at 300 °C for 4 h. The results indicate that all the branched HB‐x copolymers are promising candidates for the polymer light‐emitting diodes due to their high quantum yield and spectral stability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 Photos clearly showed that the bright green yellow light emitted from devices with the HB‐1 and HB‐four emitting layers remained essentially un‐altered despite the whole assemblies had been annealed at the respective high temperatures of 200 and 300 °C for 4 h. Therefore, it is safe to conclude that the EL spectra of the PLEDs based on the HB‐1 and HB‐4 copolymers are highly stable.