Efficient blue light-emitting polymers containing fluorene[2,3-b]benzo[d]thiophene-S,S-dioxide unit

Blue light-emitting polymers were synthesized by Suzuki polycondensation via introducing 9,9-dioctylfluorene [2,3-b]benzo [d]thiophene-S,S-dioxide (BTOF) unit into the polyfluorene and polycarbazole backbone, respectively. All the polymers show high fluorescence quantum yield and thermal stability. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymers reduce slightly with increasing the content of BTOF in the polymers. The polymers exhibit stable electroluminescence spectra with the variation of applied current densities up to 300 mA cm−2. The peak luminous efficiencies (LEmax) of 3.7 and 3.1 cd A−1 (corresponding to a maximum external quantum efficiencies (EQEmax) of 3.5 and 2.5%) with the luminances of 10085 and 19662 cd m−2 were obtained at a turn on voltage of 3.0 and 3.2 V, respectively, based on PF-BTOF30 and PCz-BTOF20 with a single-layer configuration of ITO/PEDOT:PSS/polymer/CsF/Al. Compared to the homopolymers PF and PCz, the enhanced device efficiencies about 6–8 times and the improved device lifetime exceeded an order of magnitude of the copolymers implied that introducing BTOF unit into the polymer backbone could be a promising strategy for the development of highly efficient blue light-emitting polymers.