Synthesis of copolyfluorenes containing green chromophores based on triphenylamine unit and their application in light-emitting diodes

Two series of new copolyfluorenes (PFTP, PFTT) were prepared by the Suzuki coupling reaction from two green-emitting dibromo monomers (TP-Br, TT-Br) based on trlphenylamine unit to be applied in white light electroluminescent devices. They were characterized by molecular weight determination, elemental analysis, DSC, TGA, absorption and photoluminescence spectra, and cyclic voltammetry. The estimated actual contents of the TP and TT chromophores were lower than 7.8 mol % and 1.9 mol % for PFTP and PFTT, respectively. In film state both copolyfluorenes showed photoluminescence at 400-470 and 470-600 nm originated from fluorene segments and the chromophores, respectively, due to incomplete energy transfer. Light-emitting diodes with a structure of ITO/PEDOT:PSS/ eopolymer/Ca(50 nm)/Al(100 nm) showed major emission at 493-525 nm, plus minor emission at 400-470 nm when chromophore contents were low. The maximum brightness and maximum current efficiency of PFTP2 device were 8370 cd/m ² and 1.47 cd/A, whereas those of PFTT1 device were 9440 cd/m ² and 1.77 cd/A, respectively. Tri-wavelength white-light emission was realized through blending PFTT1 with poly(9,9-dihexylfluorene) and a red-emitting iridium complex, in which the maximum brightness and CIE coordinates were 6880 cd/m² and (0.31, 0.33), respectively.