Efficient white polymer-light-emitting-diodes based on polyfluorene end-capped with yellowish-green fluorescent dye and blended with a red phosphorescent iridium complex

A novel series of blue and yellowish-green light-emitting single polymers were prepared by end-capping of low contents of 4-bromo-7H-benzo [de]naphtha[2′,3′:4,5]imidazo[2,1-a]isoquinolin-7-one (M1) into polyfluorene. Electroluminescence (EL) spectra of these polymers exhibit blue emission (λ_max = 430/460 nm) from the fluorene segments and yellowish-green emission (λ_max = 510/530 nm) from the M1 units. For the polymer (PFNAP-0.06) with the M1 unit content of 0.06 mol-%, its EL spectrum shows balanced intensities of blue emission and yellowish-green emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.25, 0.34). The maximum brightness of the device prepared from the polymer (PFNAP-0.06) is 6704 cd/m² at 10 V with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) [PEDOT:PSS]/PVK/emission layer/Ca/Ag. A new white polymer-light-emitting-diode (WPLED) can be developed from the single polymer (PFNAP-0.06) system blended with a red phosphorescent iridium complex [Bis(2-[2′-benzothienyl)-pyridinato-N,C^3′] iridium (acetylacetonate) (BtpIr)]. We were able to obtain a white-light-emission device by adjusting the molar ratio of BtpIr to PFNAP-0.06 with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) [PEDOT:PSS]/PVK/emission layer/Ca/Ag. The brightness in such a device configuration is 4030 cd/m² at 9 V with CIE coordinates of (0.32, 0.34).