Energy transfer in polyfluorene copolymer used for white-light organic light emitting device

Luminescence properties of a type of polyfluorene copolymer (PFO–DBT5) used for white-light organic light emitting device (OLED) were studied and discussed, in which a very low concentration of 0.05 mol% 4,7-bithienyl-2,1,3-benzothiadiazole (DBT) molecules were inserted in polyfluorene chain as orange-light unit. From the spectroscopic analysis of PFO–DBT5 in solution and nanoparticles, it is concluded that inter-chain Förster energy transfer from polyfluorene segments to DBT units play major role in process of white-light emission of PFO–DBT5. By measurement of electroluminescent properties, it is found that annealing of PFO–DBT5 film in vacuum is favorable for improving white-light emission owing to enhancement in inter-chain Förster energy transfer. CIE coordinates (0.38, 0.33) were obtained under the annealing temperature of 140 °C. It was found that the annealing temperature affects the luminance and efficiency of white-light OLED. The optimum annealing temperature was 100 °C.

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► Inter-chain Förster energy transfer is dominant during white-light emission of PFO–DBT5.
► Vacuum annealing of PFO–DBT5 film is favorable for improving white-light emission.
► The optimum annealing temperature is 100 °C.