Thermal and Spectral Stability of Electroluminescent Hyperbranched Copolymers Containing Tetraphenylthiophene-Quinoline-Triphenylamine Moieties

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 (T(g)s 245-315 degrees 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 (Phi(F)s) 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 degrees C. After annealing at 200 degrees C (or 300 degrees 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 T-g 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 degrees 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. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 237-249, 2012