Highly efficient and spectrally stable blue-light-emitting polyfluorenes containing a dibenzothiophene-S,S-dioxide unit

Spectrally stable blue-light-emitting polyfluorenes with high efficiency were realized via incorporating dibenzothiophene-S,S-dioxide (SO) isomer (3,7-diyl or 2,8-diyl) into the poly [9,9-bis(4-(2-ethylhexyloxy)phenyl)fluorene-2,7-diyl] (PPF) backbone. The resulting polymers have high fluorescence yield and exhibit very good thermal stability. The EL spectra of all copolymers remain almost unchanged, and no green emission is observed even at high applied current density (more than 360 mA/cm(2)) or high annealing temperature(similar to 200 degrees C). With the device configuration ITO/PEDOT:PSS/PVK/emissive layer/Ba/Al, a maximum luminous efficiency (LE) of 6.0 cd/A (corresponding to an external quantum efficiency (EQE) of 5.5%) at 69 mA/cm(2) with CIE coordinates of (0. 16, 0.19) for the polymer PPF-3,7SO20 and a maximum LE of 3.3 cd/A (EQE = 4.2%) with CIE coordinates of (0. 16, 0.08) for the polymer PPF-2,8SO5 were obtained, respectively. The results indicate that this approach is very promising to obtain spectrally stable blue-light-emitting polyfluorenes with high efficiency.