Synthesis and characterization of highly twisted and bulky tetraoctyloxybiphenyl-containing polyfluorene copolymers: toward efficient blue polymer light emitting diodes.

We have synthesized new blue light emitting random copolymers, poly(9,9'-n-dioctylfluorene-co-2,2',6,6'-tetraoctyloxybiphenyl-3,3'-diyl)s (PFTOBPs), via Ni(0)-mediated coupling reactions. The PL emission peaks of the resulting copolymers closely resembled those of the polyfluorene (PF) homopolymer. The EL devices fabricated using these copolymers exhibited highly pure blue emission with approximate 1931 CIE coordinates of (0.15, 0.15) at 1000 cd/m2. The maximum brightnesses ranged from 2000 to 12000 cd/m2 with maximum efficiencies from 0.53 to 0.97 cd/A. The efficiencies were found to increase as the fraction of TOBP in the copolymers was increased, which may result the inhibition of exciton quenching that is produced by the introduction of the highly twisted and bulky TOBP moieties into the copolymers.