Novel Hyperbranched Polyfluorenes Containing Electron-Transporting Aromatic Triazole as Branch Unit

Linear (P 1) and hyperbranched polyfluorenes (PF1−PF5) containing hole-transporting [(4-(9-carbazolyl)butoxyphenyl)] side groups and different amounts of branching triphenyl-1,2,4-triazole units (mole fraction: 0−0.22) have been synthesized to investigate hyperbranched structure−optoelectronic property relationship. The hyperbranched polymers have been characterized by NMR, FT-IR, UV−vis, GPC, thermogravimetric analysis, and fluorescence spectroscopy. They show good solubility in common organic solvents such as CHCl3, toluene, and CH2Cl2 and exhibit excellent thermal stability with decomposition temperatures higher than 446 °C. Their absorption maxima (λmax) appear at 349−378 nm (both in CHCl3 and in the film state), and furthermore, a linear relationship between 1/λmax and 1/(1 − n triazole) has been correlated. The structures of PF1−PF5 effectively suppress detrimental excimer formation (∼550 nm) under thermal annealing. However, in PF3−PF5, a new PL emission (∼520 nm) appeared after thermal annealing at 200 °C for 1 h, which was attributed to complexes formed from carbazole and triazole chromophores. Both electrochemical results and MNDO semiempirical calculation suggest that oxidation and reduction start from the side carbazole and branching triazole moieties, respectively. Two layer EL devices (ITO/PEDOT/PF1 or PF2/Al) were fabricated and their optoelectronic properties were investigated. The EL spectra of PF1 and PF2 are similar to their own PL spectra with the maximum brightness being 161 cd/m2 (at 19.1 V) and 212 cd/m2 (at 19.0 V), respectively.