Fluorescent, carrier-trapping dopants for highly efficient single-layer polyfluorene LEDs

Two fluorescent molecules with an alkynylanthracene core and pyrene end-cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enhance the hole-transport ability of the molecule and to reduce intermolecular interactions. Both compounds exhibit high thermal stabilities and narrow energy bandgaps. Single-layer polymer light-emitting diodes (PLEDs) based on poly(9,9-dioctylfluorene) (PFO) doped with the synthesized compounds exhibit excellent performance. A PLED with 0.2% of dopant 7 had a high luminance CM efficiency of 10.7 +/- 0.3 cd A(-1) as well as a brightness of 1400 cd m(-2) at a current density of 13 mA and a low turn on voltage (3.1 V) at a brightness of 10 cd m(-2). A maximum brightness of 20 500 +/- 1400 cd m(-2) at 7 V was also measured. The high efficiency of the device's performance is attributed to the good electron and hole trapping ability of the dopants, which possess suitable energy levels as compared to those of PFO.